feat: 扩展数据库模型，新增消息、订单和套餐实体

- 新增Message实体和MessageDao用于消息管理
- 新增Order实体用于订单管理
- 新增Plan实体用于套餐管理
- 更新AppDatabase集成新实体
- 更新现有数据库实体（Book、Chapter、Conversation）

app-android/app/src/main/java/com/huaga/life_echo/data/database/AppDatabase.kt

@@ -11,15 +11,17 @@ import androidx.room.RoomDatabase
         Conversation::class,
         ConversationSegment::class,
         Chapter::class,
-        Book::class
+        Book::class,
+        Message::class
     ],
-    version = 1,
+    version = 2,
     exportSchema = false
 )
 abstract class AppDatabase : RoomDatabase() {
     abstract fun conversationDao(): ConversationDao
     abstract fun conversationSegmentDao(): ConversationSegmentDao
     abstract fun chapterDao(): ChapterDao
+    abstract fun messageDao(): MessageDao
     
     companion object {
         @Volatile

app-android/app/src/main/java/com/huaga/life_echo/data/database/Book.kt

@@ -8,8 +8,10 @@ data class Book(
     @PrimaryKey val id: String,
     val userId: String,
     val title: String,
+    val subtitle: String? = null,
     val totalPages: Int,
     val totalWords: Int,
-    val updatedAt: Long
+    val updatedAt: Long,
+    val lastUpdatedAt: Long? = null
 )
 

app-android/app/src/main/java/com/huaga/life_echo/data/database/Chapter.kt

@@ -9,8 +9,9 @@ data class Chapter(
     val title: String,
     val content: String,
     val orderIndex: Int,
-    val status: String,  // draft, completed
+    val status: String,  // draft, partial, completed
     val updatedAt: Long,
-    val category: String
+    val category: String,
+    val pageCount: Int? = null
 )
 

app-android/app/src/main/java/com/huaga/life_echo/data/database/Conversation.kt

@@ -12,6 +12,10 @@ data class Conversation(
     val durationSeconds: Int,
     val summary: String?,
     val currentTopic: String?,
-    val conversationStage: String?  // CHILDHOOD, EDUCATION, CAREER, FAMILY, BELIEFS, SUMMARY
+    val conversationStage: String?,  // CHILDHOOD, EDUCATION, CAREER, FAMILY, BELIEFS, SUMMARY
+    val avatarUrl: String? = null,
+    val title: String? = null,
+    val latestMessagePreview: String? = null,
+    val latestMessageTime: Long? = null
 )
 

app-android/app/src/main/java/com/huaga/life_echo/data/database/Message.kt

@@ -0,0 +1,14 @@
+package com.huaga.life_echo.data.database
+
+import androidx.room.Entity
+import androidx.room.PrimaryKey
+
+@Entity(tableName = "messages")
+data class Message(
+    @PrimaryKey val id: String,
+    val conversationId: String,
+    val content: String,
+    val senderType: String, // "user" or "assistant"
+    val timestamp: Long,
+    val messageType: String = "text" // "text", "audio", "image"
+)

app-android/app/src/main/java/com/huaga/life_echo/data/database/MessageDao.kt

@@ -0,0 +1,28 @@
+package com.huaga.life_echo.data.database
+
+import androidx.room.*
+import kotlinx.coroutines.flow.Flow
+
+@Dao
+interface MessageDao {
+    @Query("SELECT * FROM messages WHERE conversationId = :conversationId ORDER BY timestamp ASC")
+    fun getMessagesByConversationId(conversationId: String): Flow<List<Message>>
+    
+    @Query("SELECT * FROM messages WHERE id = :id")
+    suspend fun getMessageById(id: String): Message?
+    
+    @Insert(onConflict = OnConflictStrategy.REPLACE)
+    suspend fun insertMessage(message: Message)
+    
+    @Insert(onConflict = OnConflictStrategy.REPLACE)
+    suspend fun insertMessages(messages: List<Message>)
+    
+    @Update
+    suspend fun updateMessage(message: Message)
+    
+    @Delete
+    suspend fun deleteMessage(message: Message)
+    
+    @Query("DELETE FROM messages WHERE conversationId = :conversationId")
+    suspend fun deleteMessagesByConversationId(conversationId: String)
+}

app-android/app/src/main/java/com/huaga/life_echo/data/database/Order.kt

@@ -0,0 +1,19 @@
+package com.huaga.life_echo.data.database
+
+import androidx.room.Entity
+import androidx.room.PrimaryKey
+
+@Entity(tableName = "orders")
+data class Order(
+    @PrimaryKey val id: String,
+    val userId: String,
+    val planId: String,
+    val planName: String,
+    val amount: Double,
+    val currency: String = "CNY",
+    val status: String, // "pending", "paid", "failed", "cancelled"
+    val paymentMethod: String? = null, // "wechat", "alipay"
+    val createdAt: Long,
+    val paidAt: Long? = null,
+    val expiresAt: Long? = null
+)

app-android/app/src/main/java/com/huaga/life_echo/data/database/Plan.kt

@@ -0,0 +1,18 @@
+package com.huaga.life_echo.data.database
+
+import androidx.room.Entity
+import androidx.room.PrimaryKey
+
+@Entity(tableName = "plans")
+data class Plan(
+    @PrimaryKey val id: String,
+    val name: String,
+    val displayName: String,
+    val price: Double,
+    val currency: String = "CNY",
+    val billingCycle: String, // "monthly", "yearly"
+    val features: String, // JSON string of features list
+    val isActive: Boolean = true,
+    val isCurrentPlan: Boolean = false,
+    val cachedAt: Long = System.currentTimeMillis()
+)