fix: production save errors and import HR dashboard data

Resolve invalid task creator IDs, fix API routing and file uploads on Vercel, and replace dummy seed data with HR_Dashboard import.

frontend/src/contexts/SocketContext.tsx

@@ -3,10 +3,13 @@ import { io, type Socket } from 'socket.io-client';
 
 const SocketContext = createContext<Socket | null>(null);
 
-// 같은 네트워크 팀원도 접속 가능: 백엔드 주소를 현재 페이지 호스트에서 자동 감지
+const RENDER_API = 'https://eene-dashboard-backend.onrender.com';
+
 const SOCKET_URL =
   import.meta.env.VITE_SOCKET_URL ||
-  `${window.location.protocol}//${window.location.hostname}:4000`;
+  (import.meta.env.PROD
+    ? RENDER_API
+    : `${window.location.protocol}//${window.location.hostname}:4000`);
 
 export function SocketProvider({ children }: { children: ReactNode }) {
   const socketRef = useRef<Socket | null>(null);