feat: AI 辅助修改行程（自然语言调整 + 单活动替代推荐）

- 新增 refinePlan / suggestAlternativeItems 到 ai.ts
- 新增 POST /api/blindbox/plan/refine（整体行程调整）
- 新增 POST /api/blindbox/plan/suggest-item（单活动 AI 替代 + POI 搜索）
- BlindboxPlan 底部新增自然语言输入框（方案 A）
- 编辑 modal 内新增 AI 推荐替代方案卡片（方案 B）
- export searchPois 供 suggest-item 路由复用

src/app/blindbox/[code]/page.tsx

@@ -627,6 +627,24 @@ export default function BlindboxRoomPage() {
     }
   }, [planId, profile, planDays, planAccepted, toast]);
 
+  const handleRefine = useCallback(async (instruction: string) => {
+    if (!profile || !planDays.length) return;
+    const prevDays = planDays;
+    try {
+      const res = await fetch("/api/blindbox/plan/refine", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ userId: profile.id, instruction, days: planDays }),
+      });
+      if (!res.ok) throw new Error((await res.json().catch(() => ({}))).error || "AI 调整失败");
+      const data = await res.json();
+      await handlePlanDaysChange(data.days);
+    } catch (e) {
+      setPlanDays(prevDays);
+      toast.show(e instanceof Error ? e.message : "AI 调整失败");
+    }
+  }, [profile, planDays, handlePlanDaysChange, toast]);
+
   /** Non-creator: leave room (remove membership). Creator: delete room (after confirm). */
   const handleLeaveOrDelete = async () => {
     if (!confirmLeave) {
@@ -1112,6 +1130,7 @@ export default function BlindboxRoomPage() {
                   accepted={planAccepted}
                   regenerating={generating}
                   onDaysChange={handlePlanDaysChange}
+                  onRefine={handleRefine}
                   location={room.lng != null && room.lat != null ? `${room.lng},${room.lat}` : undefined}
                   onAccept={async () => {
                     setPlanAccepted(true);