fix: support offline manual bookkeeping

frontend/lib/shared/services/local_database.dart

@@ -16,12 +16,12 @@ class LocalDatabase {
   static const _secureStorage = FlutterSecureStorage();
 
   @visibleForTesting
-  static LocalDatabase inMemoryForTesting() {
+  static LocalDatabase inMemoryForTesting({bool seedDefaults = true}) {
     final database = LocalDatabase._();
     database._database = sqlite3.openInMemory();
     database._namespace = 'test';
     database._migrate();
-    database._seedDefaults();
+    if (seedDefaults) database._seedDefaults();
     return database;
   }
 
@@ -69,7 +69,11 @@ class LocalDatabase {
       _database = database;
       _namespace = namespace;
       _migrate();
-      if (namespace == 'guest') _seedDefaults();
+      if (namespace == 'guest') {
+        _seedDefaults();
+      } else {
+        ensureDefaultCategories();
+      }
     } catch (_) {
       database.close();
       rethrow;
@@ -295,6 +299,80 @@ class LocalDatabase {
     }
   }
 
+  /// Ensures an account can still render the category picker and create a
+  /// manual transaction before its first successful category refresh.
+  ///
+  /// Account fallback IDs mirror the server's seeded system categories. The
+  /// remote refresh remains authoritative and will update these rows in place.
+  void ensureDefaultCategories({String? type}) {
+    final isGuestNamespace = _namespace == 'guest';
+    const expense = <(int, String, String, String, String, int)>[
+      (1, '餐饮', 'food', 'coral', 'expense', 0),
+      (2, '饮品', 'cup', 'cyan', 'expense', 1),
+      (3, '购物', 'cart', 'blue', 'expense', 2),
+      (4, '交通', 'metro', 'teal', 'expense', 3),
+      (5, '住房', 'house', 'sand', 'expense', 4),
+      (6, '娱乐', 'game', 'violet', 'expense', 5),
+      (7, '医疗', 'pill', 'red', 'expense', 6),
+      (8, '学习', 'book', 'indigo', 'expense', 7),
+      (9, '服饰', 'shirt', 'plum', 'expense', 8),
+      (10, '人情', 'gift', 'rose', 'expense', 9),
+      (11, '旅行', 'plane', 'sky', 'expense', 10),
+      (12, '其他', 'tag', 'graphite', 'expense', 11),
+    ];
+    const accountIncome = <(int, String, String, String, String, int)>[
+      (13, '工资', 'money', 'mint', 'income', 0),
+      (14, '兼职', 'briefcase', 'forest', 'income', 1),
+      (15, '理财', 'chart', 'navy', 'income', 2),
+      (16, '红包', 'gift', 'orange', 'income', 3),
+      (17, '报销', 'card', 'amber', 'income', 4),
+      (18, '奖金', 'sparkle', 'aqua', 'income', 5),
+      (19, '其他', 'tag', 'lime', 'income', 6),
+    ];
+    const guestIncome = <(int, String, String, String, String, int)>[
+      (101, '工资', 'money', 'mint', 'income', 10),
+      (102, '兼职', 'parttime', 'forest', 'income', 20),
+      (103, '理财', 'invest', 'navy', 'income', 30),
+      (104, '红包', 'redpacket', 'orange', 'income', 40),
+      (105, '报销', 'reimburse', 'amber', 'income', 50),
+      (106, '奖金', 'bonus', 'aqua', 'income', 60),
+      (107, '其他', 'tag', 'lime', 'income', 70),
+    ];
+    final catalogs = <String, List<(int, String, String, String, String, int)>>{
+      'expense': expense,
+      'income': isGuestNamespace ? guestIncome : accountIncome,
+    };
+    final now = DateTime.now().toUtc().toIso8601String();
+    for (final entry in catalogs.entries) {
+      if (type != null && entry.key != type) continue;
+      final active = _db.select(
+        '''SELECT 1 FROM categories
+           WHERE type = ? AND is_deleted = 0 AND is_custom = 0 LIMIT 1''',
+        [entry.key],
+      );
+      if (active.isNotEmpty) continue;
+      for (final item in entry.value) {
+        _db.execute(
+          '''
+          INSERT INTO categories
+          (id, name, icon_key, color_key, type, sort_order, is_custom, is_deleted, updated_at)
+          VALUES (?, ?, ?, ?, ?, ?, 0, 0, ?)
+          ON CONFLICT(id) DO UPDATE SET
+            name = excluded.name,
+            icon_key = excluded.icon_key,
+            color_key = excluded.color_key,
+            type = excluded.type,
+            sort_order = excluded.sort_order,
+            is_custom = 0,
+            is_deleted = 0,
+            updated_at = excluded.updated_at
+        ''',
+          [item.$1, item.$2, item.$3, item.$4, item.$5, item.$6, now],
+        );
+      }
+    }
+  }
+
   Map<String, dynamic> guestSnapshot() {
     final customCategories = _db
         .select('''