auth: use sessions

lib/core/services/storage_service.dart

@@ -7,7 +7,7 @@ import 'package:sheetless/core/models/config.dart';
 import 'package:sheetless/core/models/sheet.dart';
 
 /// Keys for secure storage (credentials and tokens).
-enum SecureStorageKey { url, jwt, email }
+enum SecureStorageKey { url, refreshToken, username }
 
 /// Data class for storing annotations with metadata.
 class StoredAnnotation {
@@ -110,7 +110,7 @@ class StorageService {
   /// while preserving server URL and email for convenience.
   Future<void> clearAllUserData() async {
     // Clear JWT token
-    await writeSecure(SecureStorageKey.jwt, null);
+    await writeSecure(SecureStorageKey.refreshToken, null);
 
     // Clear all Hive boxes
     final sheetAccessTimesBox = await Hive.openBox(_sheetAccessTimesBox);
@@ -123,7 +123,8 @@ class StorageService {
     await changeQueueBox.clear();
 
     final annotationsBox = await Hive.openBox(_annotationsBox);
-    await annotationsBox.clear();
+    await annotationsBox
+        .clear(); // TODO: this can lead to a loss of important data. Make sure the user is warned
 
     final sheetsBox = await Hive.openBox(_sheetsBox);
     await sheetsBox.clear();