fix: eliminate training panel flash on page load

- Don't restore applied state from localStorage on mount (was causing
  first-frame flash when skill was already enabled)
- Always start with applied=false; only set true on user click

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/app/lib/use-training-mode.ts

@@ -71,18 +71,10 @@ export function useModelIterationEnabled(): {
 // - 刷新页面也保持
 // 不走后端 PATCH 是为了避开 __LOCALID_* 临时 session id 导致 404
 export function useAppliedTraining(sessionId: string | null) {
+	// 不再从 localStorage 恢复 applied 状态——面板只通过用户本次会话中
+	// 显式点击 skill 按钮打开，避免页面加载时闪烁。
 	const [applied, setApplied] = useState(false);
 
-	useEffect(() => {
-		if (!sessionId || typeof window === "undefined") {
-			setApplied(false);
-			return;
-		}
-		const stored =
-			window.localStorage.getItem(APPLIED_STORAGE_PREFIX + sessionId) === "1";
-		setApplied(stored);
-	}, [sessionId]);
-
 	const setAppliedPersist = useCallback(
 		(next: boolean) => {
 			setApplied(next);