feat: 用 SSE 替代 SWR 轮询，实现房间状态实时推送

SSE 断连时自动降级为 2s 轮询，重连后切回 SSE。

src/app/api/room/[id]/swipe/route.ts

@@ -1,5 +1,6 @@
 import { NextResponse } from "next/server";
 import { atomicUpdateRoom } from "@/lib/store";
+import { notify } from "@/lib/roomEvents";
 
 export async function POST(
   req: Request,
@@ -52,6 +53,8 @@ export async function POST(
       );
     }
 
+    notify(id);
+
     return NextResponse.json({
       match: updated.match,
       likeCount: updated.likes[rid]?.length ?? 0,