feat(blindbox): AI 计划生成流式进度与渐进式文案

- 新增 runPlanGeneration 与 onProgress 回调 (blindboxPlanGen.ts)
- 新增 POST /api/blindbox/plan/stream 推送 SSE 进度事件
- 前端优先走流式接口，实时展示「分析想法→搜索地点→规划路线→快好了」
- 流式失败时回退普通 POST，客户端轮播进度文案作为后备
- 规划阶段 UI 显示 planStatusMessage 替代静态文案

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

@@ -0,0 +1,78 @@
+import { requireMembership } from "@/lib/blindbox";
+import { requireUserId } from "@/lib/api";
+import { runPlanGeneration } from "@/lib/blindboxPlanGen";
+
+function encodeSSE(event: string, data: string): string {
+  return `event: ${event}\ndata: ${data}\n\n`;
+}
+
+export async function POST(req: Request): Promise<Response> {
+  let roomId: string;
+  let userId: string;
+  let availableTime: { date: string; startHour: number; endHour: number };
+
+  try {
+    const body = await req.json();
+    roomId = body.roomId;
+    userId = body.userId;
+    availableTime = body.availableTime;
+
+    requireUserId(userId);
+    if (!roomId) {
+      return new Response(
+        JSON.stringify({ error: "roomId 不能为空" }),
+        { status: 400, headers: { "Content-Type": "application/json" } },
+      );
+    }
+
+    await requireMembership(roomId, userId);
+
+    const at = availableTime;
+    if (
+      !at?.date ||
+      typeof at.startHour !== "number" ||
+      typeof at.endHour !== "number" ||
+      at.endHour <= at.startHour
+    ) {
+      return new Response(
+        JSON.stringify({ error: "请选择有效的可用时间" }),
+        { status: 400, headers: { "Content-Type": "application/json" } },
+      );
+    }
+  } catch (e) {
+    const message = e instanceof Error ? e.message : "请求参数错误";
+    return new Response(JSON.stringify({ error: message }), {
+      status: 400,
+      headers: { "Content-Type": "application/json" },
+    });
+  }
+
+  const stream = new ReadableStream({
+    async start(controller) {
+      const encoder = new TextEncoder();
+      const push = (event: string, data: string) => {
+        controller.enqueue(encoder.encode(encodeSSE(event, data)));
+      };
+
+      try {
+        const result = await runPlanGeneration(roomId!, userId!, availableTime!, (message) => {
+          push("status", message);
+        });
+        push("plan", JSON.stringify({ id: result.id, days: result.days, createdAt: result.createdAt }));
+      } catch (e) {
+        const message = e instanceof Error ? e.message : "生成计划失败";
+        push("error", message);
+      } finally {
+        controller.close();
+      }
+    },
+  });
+
+  return new Response(stream, {
+    headers: {
+      "Content-Type": "text/event-stream",
+      "Cache-Control": "no-cache, no-transform",
+      Connection: "keep-alive",
+    },
+  });
+}