feat: 已接受契约持久化 — 保存/加载/自动展示

- PATCH /api/blindbox/plan: 接受契约时更新状态为 accepted
- GET /api/blindbox/plan: 查询房间内最近一次已接受的计划
- 进入房间时自动加载已接受计划并展示行程视图
- 修复整个周末想法不足时重复活动的问题（不足则只生成一天）

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

@@ -71,6 +71,7 @@ export default function BlindboxRoomPage() {
   const [confirmLeave, setConfirmLeave] = useState(false);
   const [leaving, setLeaving] = useState(false);
   const [locating, setLocating] = useState(false);
+  const [planId, setPlanId] = useState<string | null>(null);
   const [planDays, setPlanDays] = useState<WeekendPlanData[]>([]);
   const [planAccepted, setPlanAccepted] = useState(false);
   const [generating, setGenerating] = useState(false);
@@ -136,9 +137,28 @@ export default function BlindboxRoomPage() {
     } catch { /* ignore */ }
   }, [room]);
 
+  const fetchAcceptedPlan = useCallback(async () => {
+    const p = getCachedProfile();
+    if (!room || !p) return;
+    try {
+      const res = await fetch(`/api/blindbox/plan?roomId=${room.id}&userId=${p.id}`);
+      if (!res.ok) return;
+      const data = await res.json();
+      if (data.plan) {
+        setPlanId(data.plan.id);
+        setPlanDays(data.plan.days);
+        setPlanAccepted(true);
+        setPhase("plan_reveal");
+      }
+    } catch { /* ignore */ }
+  }, [room]);
+
   useEffect(() => {
-    if (isMember && room) fetchIdeas();
-  }, [isMember, room, fetchIdeas]);
+    if (isMember && room) {
+      fetchIdeas();
+      fetchAcceptedPlan();
+    }
+  }, [isMember, room, fetchIdeas, fetchAcceptedPlan]);
 
   useEffect(() => {
     if (isMember && inputRef.current) {
@@ -212,6 +232,7 @@ export default function BlindboxRoomPage() {
         throw new Error(data.error || "生成失败");
       }
       const data = await res.json();
+      setPlanId(data.id);
       setPlanDays(data.days);
       setPlanAccepted(false);
       setPhase("plan_reveal");
@@ -782,9 +803,18 @@ export default function BlindboxRoomPage() {
                   days={planDays}
                   accepted={planAccepted}
                   regenerating={generating}
-                  onAccept={() => {
+                  onAccept={async () => {
                     setPlanAccepted(true);
                     fireConfetti();
+                    if (planId && profile) {
+                      try {
+                        await fetch("/api/blindbox/plan", {
+                          method: "PATCH",
+                          headers: { "Content-Type": "application/json" },
+                          body: JSON.stringify({ planId, userId: profile.id }),
+                        });
+                      } catch { /* best-effort */ }
+                    }
                   }}
                   onRegenerate={() => {
                     setPhase("time_select");
@@ -792,6 +822,7 @@ export default function BlindboxRoomPage() {
                   onShare={() => setShowPlanShareCard(true)}
                   onBack={() => {
                     setPhase("pool");
+                    setPlanId(null);
                     setPlanDays([]);
                     setPlanAccepted(false);
                   }}