refactor: 兑换机制改为一图章一奖品并引入库存

- 废弃 RedemptionRule（集 N 换 1），新增 Prize 表与 Stamp 1:1 关联
- Redemption 记录直接绑定到 stampId + prizeId + prizeName 快照
- 兑换事务用 updateMany + stock>0 条件作乐观锁
- 兑换后保留 Collection 记录，图章持续彩色点亮并标记"已兑换"
- 用户端入口改为点击已收集图章弹出兑换，库存为 0 时按钮禁用
- 管理后台删除 /admin/rules，奖品编辑嵌入 StampForm

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/server/src/routes/stamps.ts

@@ -8,20 +8,25 @@ router.get("/", optionalAuth, async (req, res) => {
   const stamps = await prisma.stamp.findMany({
     where: { enabled: true },
     orderBy: { sortOrder: "asc" },
+    include: { prize: true },
   });
 
-  let collections: Set<string> = new Set();
-  let collectionMap: Map<string, Date> = new Map();
+  const collectionMap = new Map<string, Date>();
+  const redeemedSet = new Set<string>();
 
   if (req.userId) {
-    const userCollections = await prisma.collection.findMany({
-      where: { userId: req.userId },
-      select: { stampId: true, collectedAt: true },
-    });
-    userCollections.forEach((c) => {
-      collections.add(c.stampId);
-      collectionMap.set(c.stampId, c.collectedAt);
-    });
+    const [userCollections, userRedemptions] = await Promise.all([
+      prisma.collection.findMany({
+        where: { userId: req.userId },
+        select: { stampId: true, collectedAt: true },
+      }),
+      prisma.redemption.findMany({
+        where: { userId: req.userId },
+        select: { stampId: true },
+      }),
+    ]);
+    userCollections.forEach((c) => collectionMap.set(c.stampId, c.collectedAt));
+    userRedemptions.forEach((r) => redeemedSet.add(r.stampId));
   }
 
   const data = stamps.map((s) => ({
@@ -31,8 +36,18 @@ router.get("/", optionalAuth, async (req, res) => {
     imageColor: s.imageColor,
     imageGrey: s.imageGrey,
     sortOrder: s.sortOrder,
-    collected: collections.has(s.id),
+    collected: collectionMap.has(s.id),
     collectedAt: collectionMap.get(s.id)?.toISOString() ?? null,
+    redeemed: redeemedSet.has(s.id),
+    prize: s.prize
+      ? {
+          id: s.prize.id,
+          name: s.prize.name,
+          description: s.prize.description,
+          stock: s.prize.stock,
+          enabled: s.prize.enabled,
+        }
+      : null,
   }));
 
   res.json({ success: true, data });