fix: 撤销商业认证接口500错误，SELECT缺少display_name和username字段

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

backend/main.py

@@ -682,7 +682,7 @@ def revoke_business(user_id: int, body: dict = None, user=Depends(require_role("
     conn = get_db()
     conn.execute("UPDATE users SET business_verified = 0 WHERE id = ?", (user_id,))
     reason = (body or {}).get("reason", "").strip()
-    target = conn.execute("SELECT role FROM users WHERE id = ?", (user_id,)).fetchone()
+    target = conn.execute("SELECT role, display_name, username FROM users WHERE id = ?", (user_id,)).fetchone()
     if target:
         msg = "你的商业用户资格已被取消。"
         if reason: