refactor: 优化前端UI组件

- 优化ConversationListItem对话列表项组件
- 优化ChapterCard章节卡片组件
- 优化ChapterReadingView章节阅读视图
- 优化FullTextReadingView全文阅读视图

app-android/app/src/main/java/com/huaga/life_echo/ui/components/conversation/ConversationListItem.kt

@@ -1,15 +1,18 @@
 package com.huaga.life_echo.ui.components.conversation
 
 import androidx.compose.foundation.background
-import androidx.compose.foundation.clickable
+import androidx.compose.foundation.combinedClickable
+import androidx.compose.foundation.ExperimentalFoundationApi
+import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.*
 import androidx.compose.foundation.shape.CircleShape
 import androidx.compose.foundation.shape.RoundedCornerShape
-import androidx.compose.material3.Icon
-import androidx.compose.material3.IconButton
-import androidx.compose.material3.MaterialTheme
-import androidx.compose.material3.Text
+import androidx.compose.material3.*
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.clip
@@ -26,21 +29,52 @@ import com.huaga.life_echo.utils.TextUtils
 /**
  * 对话列表项组件
  */
+@OptIn(ExperimentalFoundationApi::class)
 @Composable
 fun ConversationListItem(
     conversation: ConversationListItemDto,
     onClick: () -> Unit,
     onDelete: (() -> Unit)? = null,
+    isSelected: Boolean = false,
+    isSelectionMode: Boolean = false,
+    onLongClick: (() -> Unit)? = null,
     modifier: Modifier = Modifier
 ) {
+    var showMenu by remember { mutableStateOf(false) }
+    
     Row(
         modifier = modifier
             .fillMaxWidth()
-            .clickable { onClick() }
+            .combinedClickable(
+                onClick = onClick,
+                onLongClick = onLongClick ?: {}
+            )
+            .background(
+                if (isSelected) LightPurple.copy(alpha = 0.1f)
+                else Color.Transparent
+            )
             .padding(horizontal = 16.dp, vertical = 12.dp),
         verticalAlignment = Alignment.CenterVertically
     ) {
-        // 对话信息（暂时不显示头像）
+        // 选择框（仅在多选模式时显示）
+        if (isSelectionMode) {
+            Checkbox(
+                checked = isSelected,
+                onCheckedChange = { onClick() },
+                modifier = Modifier.padding(end = 12.dp)
+            )
+        }
+        
+        // 头像
+        ConversationAvatar(
+            avatarUrl = conversation.avatarUrl,
+            isDefaultAssistant = conversation.isDefaultAssistant,
+            modifier = Modifier.size(48.dp)
+        )
+        
+        Spacer(modifier = Modifier.width(12.dp))
+        
+        // 对话信息
         Column(
             modifier = Modifier.weight(1f)
         ) {
@@ -52,11 +86,13 @@ fun ConversationListItem(
                     fontSize = 16.sp,
                     fontWeight = FontWeight.Bold,
                     color = MaterialTheme.colorScheme.onSurface,
-                    modifier = Modifier.weight(1f)
+                    modifier = Modifier.weight(1f),
+                    maxLines = 1
                 )
                 
                 // 未读消息数
                 if (conversation.unreadCount > 0) {
+                    Spacer(modifier = Modifier.width(4.dp))
                     Box(
                         modifier = Modifier
                             .size(18.dp)
@@ -77,10 +113,10 @@ fun ConversationListItem(
             Spacer(modifier = Modifier.height(4.dp))
             
             Text(
-                text = TextUtils.ellipsizeSingleLine(conversation.latestMessagePreview, 50),
+                text = TextUtils.ellipsizeSingleLine(conversation.latestMessagePreview, 100),
                 fontSize = 14.sp,
                 color = MaterialTheme.colorScheme.onSurfaceVariant,
-                maxLines = 1
+                maxLines = 2
             )
         }
         
@@ -92,20 +128,42 @@ fun ConversationListItem(
             modifier = Modifier.padding(start = 8.dp)
         )
         
-        // 删除按钮
-        if (onDelete != null) {
-            Spacer(modifier = Modifier.width(8.dp))
+        // 三个点菜单按钮（仅在非多选模式时显示）
+        if (onDelete != null && !isSelectionMode) {
+            Spacer(modifier = Modifier.width(4.dp))
+            Box {
                 IconButton(
-                onClick = { onDelete() },
+                    onClick = { showMenu = true },
                     modifier = Modifier.size(40.dp)
                 ) {
                     Icon(
-                    imageVector = AppIcons.Delete,
-                    contentDescription = "删除",
-                    tint = MaterialTheme.colorScheme.error,
+                        imageVector = AppIcons.MoreVert,
+                        contentDescription = "更多选项",
+                        tint = MaterialTheme.colorScheme.onSurfaceVariant,
                         modifier = Modifier.size(20.dp)
                     )
                 }
+                
+                DropdownMenu(
+                    expanded = showMenu,
+                    onDismissRequest = { showMenu = false }
+                ) {
+                    DropdownMenuItem(
+                        text = { Text("删除", color = MaterialTheme.colorScheme.error) },
+                        onClick = {
+                            showMenu = false
+                            onDelete()
+                        },
+                        leadingIcon = {
+                            Icon(
+                                imageVector = AppIcons.Delete,
+                                contentDescription = null,
+                                tint = MaterialTheme.colorScheme.error
+                            )
+                        }
+                    )
+                }
+            }
         }
     }
 }
@@ -122,24 +180,32 @@ fun ConversationAvatar(
     Box(
         modifier = modifier
             .clip(RoundedCornerShape(8.dp))
-            .background(LightPurple),
+            .background(if (isDefaultAssistant) LightPurple else MaterialTheme.colorScheme.primaryContainer),
         contentAlignment = Alignment.Center
     ) {
-        if (avatarUrl != null) {
+        if (avatarUrl != null && !isDefaultAssistant) {
             // TODO: 使用Coil或Glide加载网络图片
             // 暂时显示图标
             Icon(
                 imageVector = AppIcons.Conversation,
                 contentDescription = "头像",
                 tint = Color.White,
-                modifier = Modifier.size(24.dp)
+                modifier = Modifier.size(32.dp)
+            )
+        } else if (isDefaultAssistant) {
+            // 回忆录助手使用应用图标（使用Book图标作为占位符，实际应该加载应用图标）
+            Icon(
+                imageVector = AppIcons.Book,
+                contentDescription = "回忆录助手",
+                tint = Color.White,
+                modifier = Modifier.size(32.dp)
             )
         } else {
             Icon(
-                imageVector = if (isDefaultAssistant) AppIcons.Book else AppIcons.Conversation,
+                imageVector = AppIcons.Conversation,
                 contentDescription = "头像",
                 tint = Color.White,
-                modifier = Modifier.size(24.dp)
+                modifier = Modifier.size(32.dp)
             )
         }
     }

app-android/app/src/main/java/com/huaga/life_echo/ui/components/memoir/ChapterCard.kt

@@ -9,7 +9,6 @@ import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material3.Card
 import androidx.compose.material3.CardDefaults
 import androidx.compose.material3.HorizontalDivider
-import androidx.compose.material3.Icon
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
 import androidx.compose.runtime.*
@@ -22,8 +21,9 @@ import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.unit.sp
 import com.huaga.life_echo.network.models.ChapterDto
-import com.huaga.life_echo.ui.icons.AppIcons
+import com.huaga.life_echo.ui.components.common.MarkdownText
 import com.huaga.life_echo.ui.theme.LightPurple
+import com.huaga.life_echo.utils.TextUtils
 
 /**
  * 章节卡片组件（可展开显示详细内容）
@@ -72,8 +72,8 @@ fun ChapterCard(
                     contentAlignment = Alignment.Center
                 ) {
                     Text(
-                        text = String.format("%02d", chapter.order_index),
-                        fontSize = 18.sp,
+                        text = "第${chapter.order_index}章",
+                        fontSize = 14.sp,
                         fontWeight = FontWeight.Bold,
                         color = Color.White
                     )
@@ -98,14 +98,6 @@ fun ChapterCard(
                         color = MaterialTheme.colorScheme.onSurfaceVariant
                     )
                 }
-                
-                // 展开/收起图标
-                Icon(
-                    imageVector = if (isExpanded) AppIcons.ExpandLess else AppIcons.ExpandMore,
-                    contentDescription = if (isExpanded) "收起" else "展开",
-                    tint = MaterialTheme.colorScheme.onSurfaceVariant,
-                    modifier = Modifier.size(24.dp)
-                )
             }
             
             // 展开时显示详细内容
@@ -118,11 +110,18 @@ fun ChapterCard(
                         .fillMaxWidth()
                         .padding(16.dp)
                 ) {
-                    Text(
-                        text = chapter.content,
-                        fontSize = 14.sp,
-                        color = MaterialTheme.colorScheme.onSurface,
-                        lineHeight = 22.sp
+                    // 使用Markdown渲染，并移除{{IMAGE}}占位符（如果没有图片）
+                    val processedContent = TextUtils.removeImagePlaceholders(
+                        chapter.content,
+                        hasImages = chapter.images.isNotEmpty()
+                    )
+                    
+                    MarkdownText(
+                        content = processedContent,
+                        modifier = Modifier.fillMaxWidth(),
+                        textColor = MaterialTheme.colorScheme.onSurface,
+                        fontSize = 14,
+                        lineHeight = 22
                     )
                     Spacer(modifier = Modifier.height(12.dp))
                     // 查看详情按钮

app-android/app/src/main/java/com/huaga/life_echo/ui/components/memoir/ChapterReadingView.kt

@@ -15,6 +15,7 @@ import androidx.compose.ui.unit.sp
 import com.huaga.life_echo.network.models.ChapterContentDto
 import com.huaga.life_echo.ui.components.common.MarkdownText
 import com.huaga.life_echo.ui.theme.LightPurple
+import com.huaga.life_echo.utils.TextUtils
 
 /**
  * 章节阅读视图组件
@@ -47,9 +48,13 @@ fun ChapterReadingView(
                 modifier = Modifier.padding(bottom = 24.dp)
             )
             
-            // 正文内容（支持 Markdown）
+            // 正文内容（支持 Markdown，移除{{IMAGE}}占位符如果没有图片）
+            val processedContent = TextUtils.removeImagePlaceholders(
+                chapter.content,
+                hasImages = chapter.images.isNotEmpty()
+            )
             MarkdownText(
-                content = chapter.content,
+                content = processedContent,
                 modifier = Modifier.padding(bottom = 16.dp),
                 textColor = MaterialTheme.colorScheme.onSurface,
                 fontSize = 16,

app-android/app/src/main/java/com/huaga/life_echo/ui/components/memoir/FullTextReadingView.kt

@@ -20,6 +20,7 @@ import com.huaga.life_echo.network.models.ChapterContentDto
 import com.huaga.life_echo.ui.components.common.MarkdownText
 import com.huaga.life_echo.ui.icons.AppIcons
 import com.huaga.life_echo.ui.theme.LightPurple
+import com.huaga.life_echo.utils.TextUtils
 
 /**
  * 全文阅读视图组件
@@ -61,9 +62,13 @@ fun FullTextReadingView(
                         modifier = Modifier.padding(bottom = 16.dp)
                     )
                     
-                    // 章节内容（支持 Markdown）
+                    // 章节内容（支持 Markdown，移除{{IMAGE}}占位符如果没有图片）
+                    val processedContent = TextUtils.removeImagePlaceholders(
+                        chapter.content,
+                        hasImages = chapter.images.isNotEmpty()
+                    )
                     MarkdownText(
-                        content = chapter.content,
+                        content = processedContent,
                         modifier = Modifier.padding(bottom = 16.dp),
                         textColor = MaterialTheme.colorScheme.onSurface,
                         fontSize = 16,