Backup panel PostgreSQL database as .sql dump (v2.6.2).

Co-authored-by: Cursor <cursoragent@cursor.com>

db/__init__.py

@@ -1,5 +1,6 @@
 """Database package for Amnezia Web Panel (PostgreSQL 17)."""
 
+from .backup import backup_filename, export_database_sql, restore_database_sql
 from .connection import close_pool, get_database_url, init_schema
 from .store import (
     clear_tunnel_state,
@@ -14,15 +15,18 @@ from .store import (
 )
 
 __all__ = [
+    'backup_filename',
     'clear_tunnel_state',
     'close_pool',
     'ensure_db_ready',
     'export_data_dict',
+    'export_database_sql',
     'get_database_url',
     'import_from_json_file',
     'init_schema',
     'load_data',
     'load_tunnel_state',
+    'restore_database_sql',
     'save_data',
     'save_tunnel_state',
     'update_tunnel_state',