feat: add customer service agent entry in Settings

- "天工客服" agent (ID: 3490efa8) created on backend, status: published
- Settings > Account section now has "联系客服" button
- Tap navigates to chat with the CS agent directly

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

android/app/src/main/java/com/tiangong/aiagent/ui/navigation/NavGraph.kt

@@ -24,6 +24,9 @@ import com.tiangong.aiagent.ui.settings.AboutScreen
 import com.tiangong.aiagent.ui.settings.AccountSecurityScreen
 import com.tiangong.aiagent.ui.settings.SettingsScreen
 
+private const val CS_AGENT_ID = "3490efa8-330d-458d-a26e-0b6c1d72e6f4"
+private const val CS_AGENT_NAME = "天工客服"
+
 object Routes {
     const val LOGIN = "login"
     const val REGISTER = "register"
@@ -132,6 +135,9 @@ fun NavGraph(
         }
 
         composable(Routes.SETTINGS) {
+            val chatViewModel: ChatViewModel = hiltViewModel(
+                navController.getBackStackEntry(Routes.CHAT)
+            )
             SettingsScreen(
                 onBack = { navController.popBackStack() },
                 onLogout = {
@@ -140,7 +146,16 @@ fun NavGraph(
                     }
                 },
                 onNavigateToAbout = { navController.navigate(Routes.ABOUT) },
-                onNavigateToAccountSecurity = { navController.navigate(Routes.ACCOUNT_SECURITY) }
+                onNavigateToAccountSecurity = { navController.navigate(Routes.ACCOUNT_SECURITY) },
+                onContactSupport = {
+                    val csAgent = Agent(
+                        id = CS_AGENT_ID,
+                        name = CS_AGENT_NAME,
+                        description = "天工智能体平台官方客服"
+                    )
+                    chatViewModel.switchAgent(csAgent)
+                    navController.popBackStack()
+                }
             )
         }
 

android/app/src/main/java/com/tiangong/aiagent/ui/settings/SettingsScreen.kt

@@ -171,6 +171,7 @@ fun SettingsScreen(
     onLogout: () -> Unit,
     onNavigateToAbout: (() -> Unit)? = null,
     onNavigateToAccountSecurity: (() -> Unit)? = null,
+    onContactSupport: (() -> Unit)? = null,
     viewModel: SettingsViewModel = hiltViewModel()
 ) {
     var showLogoutDialog by remember { mutableStateOf(false) }
@@ -227,6 +228,18 @@ fun SettingsScreen(
                 )
             }
 
+            if (onContactSupport != null) {
+                HorizontalDivider(modifier = Modifier.padding(horizontal = 16.dp))
+                ListItem(
+                    headlineContent = { Text("联系客服") },
+                    supportingContent = { Text("有问题？随时联系我们") },
+                    leadingContent = {
+                        Icon(Icons.Default.Help, contentDescription = null)
+                    },
+                    modifier = Modifier.clickable { onContactSupport() }
+                )
+            }
+
             HorizontalDivider(modifier = Modifier.padding(horizontal = 16.dp))
 
             // Preferences section