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/shared/src/types.ts

@@ -4,6 +4,14 @@ export type ApiResponse<T = unknown> = {
   error?: { code: string; message: string };
 };
 
+export type PrizeInfo = {
+  id: string;
+  name: string;
+  description: string | null;
+  stock: number;
+  enabled: boolean;
+};
+
 export type StampWithStatus = {
   id: string;
   name: string;
@@ -13,19 +21,15 @@ export type StampWithStatus = {
   sortOrder: number;
   collected: boolean;
   collectedAt: string | null;
-};
-
-export type RedemptionRuleInfo = {
-  id: string;
-  name: string;
-  description: string | null;
-  threshold: number;
+  redeemed: boolean;
+  prize: PrizeInfo | null;
 };
 
 export type RedemptionRecord = {
   id: string;
-  ruleName: string;
-  stampCount: number;
+  stampId: string;
+  stampName: string;
+  prizeName: string;
   redeemedAt: string;
 };