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/web/src/App.tsx

@@ -11,7 +11,6 @@ import Dashboard from "./admin/Dashboard";
 import StampList from "./admin/StampList";
 import ArticleList from "./admin/ArticleList";
 import MusicList from "./admin/MusicList";
-import RuleList from "./admin/RuleList";
 import UsersList from "./admin/UsersList";
 import RedemptionLog from "./admin/RedemptionLog";
 
@@ -39,7 +38,6 @@ export default function App() {
             <Route path="/admin/stamps" element={<StampList />} />
             <Route path="/admin/articles" element={<ArticleList />} />
             <Route path="/admin/music" element={<MusicList />} />
-            <Route path="/admin/rules" element={<RuleList />} />
             <Route path="/admin/users" element={<UsersList />} />
             <Route path="/admin/redemptions" element={<RedemptionLog />} />
           </Route>