fix: username_changed字段加入认证查询，改名后铅笔和通知按钮正确隐藏

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/main.py

@@ -63,7 +63,7 @@ def get_current_user(request: Request):
     if not token:
         return ANON_USER
     conn = get_db()
-    user = conn.execute("SELECT id, username, role, display_name, password, business_verified FROM users WHERE token = ?", (token,)).fetchone()
+    user = conn.execute("SELECT id, username, role, display_name, password, business_verified, username_changed FROM users WHERE token = ?", (token,)).fetchone()
     conn.close()
     if not user:
         return ANON_USER