fix: preserve takeover and share token integrity

digital-avatar-app/backend/database.py

@@ -38,8 +38,9 @@ def init_db():
         ("authorizations", "takeover_enabled", "BOOLEAN DEFAULT 0"),
         ("authorizations", "takeover_mode", "VARCHAR DEFAULT 'immediate'"),
         ("authorizations", "takeover_delay_seconds", "INTEGER DEFAULT 30"),
-        ("avatars", "share_token", "VARCHAR DEFAULT ''"),
+        ("avatars", "share_token", "VARCHAR DEFAULT NULL"),
     )
+    _normalize_optional_unique_values()
 
 
 def _try_add_columns(*cols):
@@ -51,3 +52,8 @@ def _try_add_columns(*cols):
             except Exception:
                 # 列已存在（或全新库由 create_all 建好）则忽略
                 pass
+
+
+def _normalize_optional_unique_values():
+    with engine.begin() as conn:
+        conn.exec_driver_sql("UPDATE avatars SET share_token = NULL WHERE share_token = ''")