feat: add Shaarli account config and 401 logout

Add a "Compte Shaarli" settings section to edit the server URL and
API secret with online re-validation, plus a logout action.

Detect 401 responses from the Shaarli API via SessionManager, clear
stored credentials and return the user to the login screen.

app/src/main/java/com/shaarit/presentation/nav/NavGraph.kt

@@ -12,6 +12,8 @@ import androidx.navigation.compose.composable
 import androidx.navigation.compose.rememberNavController
 import androidx.navigation.navArgument
 import androidx.navigation.navDeepLink
+import com.shaarit.core.network.SessionManager
+import com.shaarit.core.storage.TokenManager
 import java.net.URLEncoder
 
 sealed class Screen(val route: String) {
@@ -60,6 +62,8 @@ sealed class Screen(val route: String) {
 @Composable
 fun AppNavGraph(
     startDestination: String = Screen.Login.route,
+    sessionManager: SessionManager? = null,
+    tokenManager: TokenManager? = null,
     shareUrl: String? = null,
     shareTitle: String? = null,
     shareDescription: String? = null,
@@ -70,7 +74,24 @@ fun AppNavGraph(
 ) {
     val navController = rememberNavController()
     val context = LocalContext.current
-    
+
+    // On a 401 from the Shaarli API, the stored API secret is stale (it changed server-side).
+    // Wipe the credentials and send the user back to the login screen.
+    if (sessionManager != null && tokenManager != null) {
+        androidx.compose.runtime.LaunchedEffect(sessionManager) {
+            sessionManager.unauthorized.collect {
+                tokenManager.clearToken()
+                tokenManager.clearApiSecret()
+                val currentRoute = navController.currentBackStackEntry?.destination?.route
+                if (currentRoute != Screen.Login.route) {
+                    navController.navigate(Screen.Login.route) {
+                        popUpTo(navController.graph.id) { inclusive = true }
+                        launchSingleTop = true
+                    }
+                }
+            }
+        }
+    }
     // If user is already logged in and has share data, navigate directly to Add screen
     val hasShareData = shareUrl != null || (isFileShare && shareTitle != null)
     androidx.compose.runtime.LaunchedEffect(hasShareData) {
@@ -292,7 +313,13 @@ fun AppNavGraph(
         ) {
             com.shaarit.presentation.settings.SettingsScreen(
                 onNavigateBack = { navController.popBackStack() },
-                onNavigateToDashboard = { navController.navigate(Screen.Dashboard.route) }
+                onNavigateToDashboard = { navController.navigate(Screen.Dashboard.route) },
+                onNavigateToLogin = {
+                    navController.navigate(Screen.Login.route) {
+                        popUpTo(navController.graph.id) { inclusive = true }
+                        launchSingleTop = true
+                    }
+                }
             )
         }