feat: 盲盒想法输入增加 AI 灵感推荐

输入框下方展示灵感建议标签，点击即填入，降低创作门槛：
- 房间有 ≥2 条想法时调用 DeepSeek 生成贴合调性的推荐
- 想法不足或 AI 失败时 fallback 到 18 条静态灵感随机选 4 条
- 提交新想法后自动刷新推荐，支持手动换一批

src/app/api/blindbox/suggest/route.ts

@@ -0,0 +1,35 @@
+import { NextResponse } from "next/server";
+import { prisma } from "@/lib/prisma";
+import { requireMembership } from "@/lib/blindbox";
+import { apiHandler, ApiError, requireUserId } from "@/lib/api";
+import { suggestIdeas } from "@/lib/ai";
+
+export const GET = apiHandler(async (req) => {
+  const { searchParams } = new URL(req.url);
+  const roomId = searchParams.get("roomId");
+  const userId = searchParams.get("userId");
+
+  requireUserId(userId);
+  if (!roomId) throw new ApiError("roomId 不能为空");
+
+  await requireMembership(roomId, userId!);
+
+  const recentIdeas = await prisma.blindBoxIdea.findMany({
+    where: { roomId, status: "in_pool" },
+    orderBy: { createdAt: "desc" },
+    take: 10,
+    select: { content: true },
+  });
+
+  if (recentIdeas.length < 2) {
+    return NextResponse.json({ suggestions: [], source: "none" });
+  }
+
+  const suggestions = await suggestIdeas(recentIdeas.map((i) => i.content));
+
+  if (suggestions.length === 0) {
+    return NextResponse.json({ suggestions: [], source: "none" });
+  }
+
+  return NextResponse.json({ suggestions, source: "ai" });
+});