refactor(P2/P3): 完成全部7批重构 — 模块化、SSE退避、无障碍、Zod校验、Server组件、Room关系化

批次A：重命名 + 路由拆分
- store.ts → roomRepository.ts，更新全部 import
- blindbox/plan/route.ts 精简为薄路由，业务逻辑抽取到 planActions.ts / planQueries.ts

批次B：blindboxPlanGen.ts 拆分（710行 → src/lib/plan/）
- agentPlan.ts：Agent 工具调用与系统提示
- legacyPlan.ts：非 Agent 备用生成逻辑
- ideaSelection.ts：Idea 筛选与 Slot 映射
- transitEnrichment.ts：交通信息查询与填充
- index.ts：runPlanGeneration 主入口

批次C：SSE 连接稳定性
- useRoomPolling.ts 加入指数退避重连（上限60s，含Jitter）
- plan/stream/route.ts 添加30s心跳 + abort信号清理

批次D：无障碍修复
- Modal：role=dialog、aria-modal、aria-labelledby
- AuthModal：aria-label关闭按钮、tablist/tab/aria-selected
- PlanItemEditModal、QrInviteModal：补全aria-label
- BlindboxPlan：图标按钮aria-label

批次E：Zod 引入
- src/lib/schemas/ai.ts：AI返回值 Schema（IdeaTagsSchema等5个）
- src/lib/schemas/requests.ts：请求体 Schema
- ai.ts 手工验证替换为 Zod safeParse

批次F：Server Components
- achievements/page.tsx → Server Component + AchievementsClient.tsx
- profile/page.tsx → Server Component + ProfileClient.tsx

批次G：Room 关系化模型
- prisma/schema.prisma：新增 RoomMember、RoomRestaurant、RoomLike、RoomSwipe 4张表
- migration：20260302010000_room_relational_model
- roomRepository.ts 完整重写（关系查询+应用锁）
- buildRoomStatus.ts 适配关系查询

测试：全部329个用例通过，修复68个因auth mock缺失导致的测试失败

src/app/api/blindbox/plan/stream/route.ts

@@ -49,13 +49,33 @@ export async function POST(req: NextRequest): Promise<Response> {
     });
   }
 
+  const signal = req.signal;
+
   const stream = new ReadableStream({
     async start(controller) {
       const encoder = new TextEncoder();
+
+      let closed = false;
       const push = (event: string, data: string) => {
+        if (closed) return;
         controller.enqueue(encoder.encode(encodeSSE(event, data)));
       };
 
+      const cleanup = () => {
+        if (closed) return;
+        closed = true;
+        clearInterval(heartbeatId);
+        try { controller.close(); } catch {}
+      };
+
+      // 30s heartbeat to prevent proxy disconnects
+      const heartbeatId = setInterval(() => {
+        push("heartbeat", "ping");
+      }, 30_000);
+
+      // Clean up when client disconnects
+      signal.addEventListener("abort", cleanup);
+
       try {
         const result = await runPlanGeneration(roomId, userId, availableTime, (message) => {
           push("status", message);
@@ -65,7 +85,7 @@ export async function POST(req: NextRequest): Promise<Response> {
         const message = e instanceof Error ? e.message : "生成计划失败";
         push("error", message);
       } finally {
-        controller.close();
+        cleanup();
       }
     },
   });