refactor(auth): Preserve server configs during logout for seamless re-login

lib/core/auth/auth_state_manager.dart

@@ -775,7 +775,10 @@ class AuthStateManager extends _$AuthStateManager {
     }
   }
 
-  /// Logout user and clear all data including server configs and custom headers
+  /// Logout user and clear auth data while preserving server configuration.
+  /// Server settings (URL, custom headers, self-signed cert) are kept so users
+  /// can quickly re-login. Users can navigate to server connection page to
+  /// change server settings if needed.
   Future<void> logout() async {
     _update(
       (current) =>
@@ -797,17 +800,16 @@ class AuthStateManager extends _$AuthStateManager {
         }
       }
 
-      // Clear all local auth data (including server configs with custom headers)
+      // Clear auth data but preserve server configs (URL, headers, cert settings)
       final storage = ref.read(optimizedStorageServiceProvider);
       await storage.clearAuthData();
       _updateApiServiceToken(null);
 
-      // Clear active server to force return to server connection page
-      await storage.setActiveServerId(null);
+      // Keep active server ID so router redirects to sign-in page, not server
+      // connection page. Users can navigate to server settings if they need to
+      // change server configuration.
 
-      // Invalidate all auth-related providers to clear cached data
-      ref.invalidate(activeServerProvider);
-      ref.invalidate(serverConfigsProvider);
+      // Invalidate tools provider to clear cached data
       ref.invalidate(toolsListProvider);
 
       // Clear auth cache manager
@@ -825,7 +827,7 @@ class AuthStateManager extends _$AuthStateManager {
       );
 
       DebugLogger.auth(
-        'Logout complete - all data cleared including server configs and custom headers',
+        'Logout complete - auth data cleared, server config preserved for quick re-login',
       );
     } catch (e, stack) {
       DebugLogger.error(
@@ -845,9 +847,7 @@ class AuthStateManager extends _$AuthStateManager {
           error: clearError,
         );
       }
-      await storage.setActiveServerId(null);
-      ref.invalidate(activeServerProvider);
-      ref.invalidate(serverConfigsProvider);
+      // Keep active server ID for redirect to sign-in page
       _cacheManager.clearAuthCache();
 
       _update(

lib/core/router/app_router.dart

@@ -145,7 +145,10 @@ class RouterNotifier extends ChangeNotifier {
         return location == Routes.splash ? null : Routes.splash;
       case AuthNavigationState.needsLogin:
         if (location == Routes.connectionIssue) return null;
-        return null;
+        // Redirect to authentication page if not already on an auth route
+        // This handles the post-logout case where we want sign-in, not server setup
+        if (_isAuthLocation(location)) return null;
+        return Routes.authentication;
       case AuthNavigationState.error:
         final authSnapshot = ref
             .read(authStateManagerProvider)

lib/core/services/optimized_storage_service.dart

@@ -762,13 +762,13 @@ class OptimizedStorageService {
   // ---------------------------------------------------------------------------
   // Batch operations
   // ---------------------------------------------------------------------------
-  /// Clear all authentication-related data including credentials, tokens,
-  /// server configurations, and custom headers
+  /// Clear authentication-related data (tokens, credentials, user data).
+  /// Server configurations (URL, custom headers, self-signed cert settings)
+  /// are preserved to allow quick re-login.
   Future<void> clearAuthData() async {
     await Future.wait([
       deleteAuthToken(),
       deleteSavedCredentials(),
-      _preferencesBox.delete(_activeServerIdKey),
       _cachesBox.delete(_localUserKey),
       _cachesBox.delete(_localUserAvatarKey),
       _cachesBox.delete(_localBackendConfigKey),
@@ -776,19 +776,16 @@ class OptimizedStorageService {
       _cachesBox.delete(_localToolsKey),
       _cachesBox.delete(_localDefaultModelKey),
       _cachesBox.delete(_localModelsKey),
-      // Clear server configurations (which include custom headers)
-      _secureCredentialStorage.clearAll(),
+      // Note: Server configs are NOT cleared - they persist across logouts
+      // so users can quickly re-login without re-entering server details
     ]);
 
     _cacheManager.invalidateMatching(
-      (key) =>
-          key.contains('auth') ||
-          key.contains('credentials') ||
-          key.contains('server'),
+      (key) => key.contains('auth') || key.contains('credentials'),
     );
 
     DebugLogger.log(
-      'Auth data cleared in batch operation (including server configs and custom headers)',
+      'Auth data cleared (server configs preserved for quick re-login)',
       scope: 'storage/optimized',
     );
   }