feat: 统一调试模块 debug.ts，VITE_DEBUG 环境变量控制调试面板显隐

- 新增 services/debug.ts: isDebug()/debugLog()/getDebugLogs()
- .env 中 VITE_DEBUG=true 开启调试，false 关闭
- LoginPage 使用 debugLog() 记录登录流程
- ProfilePage 通过 isDebug() 控制调试面板显隐
- .env.example 同步更新

frontend/src/app/pages/ProfilePage.tsx

@@ -24,6 +24,7 @@ import { Button } from "../components/ui/button";
 import { Card } from "../components/ui/card";
 import { Badge } from "../components/ui/badge";
 import { useUser, getPregnancyStage } from "../context/UserContext";
+import { isDebug, getDebugLogs } from "../services/debug";
 
 interface UserInfo {
   name: string;
@@ -187,8 +188,23 @@ export function ProfilePage() {
     </div>
   );
 
+  // 🐞 调试面板（VITE_DEBUG=true 时显示）
+  const [debugLog] = useState<string[]>(() => isDebug() ? getDebugLogs() : []);
+  const [showDebug, setShowDebug] = useState(false);
+
   return (
-    <div className="min-h-dvh bg-morandi-50">
+    <div className="min-h-dvh bg-morandi-50 pb-20">
+      {/* 🐞 调试面板 */}
+      {debugLog.length > 0 && (
+        <div className="bg-black/80 text-white text-xs font-mono p-3">
+          <button onClick={() => setShowDebug(!showDebug)} className="text-yellow-400 font-bold mb-1">
+            🐞 {showDebug ? '收起' : '展开'}调试日志 ({debugLog.length}条)
+          </button>
+          {showDebug && debugLog.map((line, i) => (
+            <div key={i} className="text-green-300 break-all">{line}</div>
+          ))}
+        </div>
+      )}
       {/* 顶部导航 */}
       <div className="bg-white border-b border-gray-100 sticky top-0 z-10">
         <div className="mx-auto px-4 py-4 flex items-center justify-between">