feat(app): смена сервера API и очистка данных устройства при выходе

Адрес бэкенда хранится в shared_preferences и читается до runApp; switchApiBaseUrl сбрасывает токены и кэш старого сервера. Выход стирает refresh-токен и sqlite-кэш ответов. Экран настроек переделан под разделы.

app/lib/core/cache/response_cache.dart

@@ -38,7 +38,8 @@ class ResponseCacheDatabase extends _$ResponseCacheDatabase {
 
   /// Replaces whatever was cached for [requestKey] — one row per endpoint+params,
   /// never a history.
-  Future<void> put(String requestKey, Object? body) => into(cachedResponses).insertOnConflictUpdate(
+  Future<void> put(String requestKey, Object? body) =>
+      into(cachedResponses).insertOnConflictUpdate(
         CachedResponsesCompanion.insert(
           requestKey: requestKey,
           body: jsonEncode(body),
@@ -46,6 +47,9 @@ class ResponseCacheDatabase extends _$ResponseCacheDatabase {
         ),
       );
 
+  /// Drops every cached body — on sign-out, so the next account (or nobody) never sees them.
+  Future<void> clear() => delete(cachedResponses).go();
+
   /// The body last stored for [requestKey], or null if this endpoint+params was
   /// never fetched successfully on this device.
   Future<CacheEntry?> get(String requestKey) async {
@@ -63,9 +67,9 @@ class ResponseCacheDatabase extends _$ResponseCacheDatabase {
 /// the compiled assets it loads there (regenerate with `just app-web-assets`
 /// whenever the `drift`/`sqlite3` package versions change).
 QueryExecutor _openConnection() => driftDatabase(
-      name: 'response_cache',
-      web: DriftWebOptions(
-        sqlite3Wasm: Uri.parse('sqlite3.wasm'),
-        driftWorker: Uri.parse('drift_worker.js'),
-      ),
-    );
+  name: 'response_cache',
+  web: DriftWebOptions(
+    sqlite3Wasm: Uri.parse('sqlite3.wasm'),
+    driftWorker: Uri.parse('drift_worker.js'),
+  ),
+);