feat: 新增法律文档屏幕和导航

- 新增LegalDocumentScreen法律文档屏幕
- 更新AppNavigation导航结构

app-android/app/src/main/java/com/huaga/life_echo/navigation/AppNavigation.kt

@@ -27,6 +27,8 @@ sealed class Screen(val route: String) {
     object FAQ : Screen("faq")
     object Feedback : Screen("feedback")
     object About : Screen("about")
+    object Terms : Screen("terms")
+    object Privacy : Screen("privacy")
 }
 
 @OptIn(ExperimentalAnimationApi::class)
@@ -149,6 +151,30 @@ fun AppNavigation(
         ) {
             AboutScreen(navController = navController)
         }
+        composable(
+            route = Screen.Terms.route,
+            enterTransition = { slideInHorizontally() },
+            exitTransition = { slideOutHorizontally() },
+            popEnterTransition = { slideInHorizontallyFromLeft() },
+            popExitTransition = { slideOutHorizontallyToRight() }
+        ) {
+            LegalDocumentScreen(
+                documentType = com.huaga.life_echo.ui.screens.LegalDocumentType.TERMS,
+                onNavigateBack = { navController.popBackStack() }
+            )
+        }
+        composable(
+            route = Screen.Privacy.route,
+            enterTransition = { slideInHorizontally() },
+            exitTransition = { slideOutHorizontally() },
+            popEnterTransition = { slideInHorizontallyFromLeft() },
+            popExitTransition = { slideOutHorizontallyToRight() }
+        ) {
+            LegalDocumentScreen(
+                documentType = com.huaga.life_echo.ui.screens.LegalDocumentType.PRIVACY,
+                onNavigateBack = { navController.popBackStack() }
+            )
+        }
         composable(
             route = Screen.Login.route,
             enterTransition = { fadeInTransition() },
@@ -169,6 +195,12 @@ fun AppNavigation(
                 },
                 onNavigateToResetPassword = {
                     navController.navigate(Screen.ResetPassword.route)
+                },
+                onNavigateToTerms = {
+                    navController.navigate(Screen.Terms.route)
+                },
+                onNavigateToPrivacy = {
+                    navController.navigate(Screen.Privacy.route)
                 }
             )
         }
@@ -182,6 +214,12 @@ fun AppNavigation(
             RegisterScreen(
                 onRegisterSuccess = {
                     navController.popBackStack()
+                },
+                onNavigateToTerms = {
+                    navController.navigate(Screen.Terms.route)
+                },
+                onNavigateToPrivacy = {
+                    navController.navigate(Screen.Privacy.route)
                 }
             )
         }

app-android/app/src/main/java/com/huaga/life_echo/ui/screens/LegalDocumentScreen.kt

@@ -0,0 +1,75 @@
+package com.huaga.life_echo.ui.screens
+
+import android.webkit.WebView
+import android.webkit.WebViewClient
+import androidx.compose.foundation.layout.*
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.ArrowBack
+import androidx.compose.material3.*
+import androidx.compose.runtime.*
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.viewinterop.AndroidView
+import com.huaga.life_echo.config.AppConfig
+
+/**
+ * 法律文档页面（用户协议或隐私政策）
+ * 使用WebView显示后端返回的HTML内容
+ */
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun LegalDocumentScreen(
+    documentType: LegalDocumentType,
+    onNavigateBack: () -> Unit
+) {
+    val context = LocalContext.current
+    val url = "${AppConfig.BASE_URL}/api/legal/${documentType.endpoint}"
+    
+    Scaffold(
+        topBar = {
+            TopAppBar(
+                title = { Text(documentType.title) },
+                navigationIcon = {
+                    IconButton(onClick = onNavigateBack) {
+                        Icon(
+                            imageVector = Icons.Default.ArrowBack,
+                            contentDescription = "返回"
+                        )
+                    }
+                },
+                colors = TopAppBarDefaults.topAppBarColors(
+                    containerColor = MaterialTheme.colorScheme.surface,
+                    titleContentColor = MaterialTheme.colorScheme.onSurface
+                )
+            )
+        }
+    ) { paddingValues ->
+        AndroidView(
+            factory = { ctx ->
+                WebView(ctx).apply {
+                    webViewClient = WebViewClient()
+                    settings.javaScriptEnabled = true
+                    settings.domStorageEnabled = true
+                    settings.loadWithOverviewMode = true
+                    settings.useWideViewPort = true
+                    settings.builtInZoomControls = true
+                    settings.displayZoomControls = false
+                    loadUrl(url)
+                }
+            },
+            modifier = Modifier
+                .fillMaxSize()
+                .padding(paddingValues)
+        )
+    }
+}
+
+/**
+ * 法律文档类型
+ */
+enum class LegalDocumentType(val title: String, val endpoint: String) {
+    TERMS("用户协议", "terms"),
+    PRIVACY("隐私政策", "privacy")
+}