feat: 消息推送自定义模板与独立设置页

后端:
- 新增通知模板表与实体、DTO、Repository、NotificationTemplateService
- 支持 {{variable}} 模板语法，提供模板类型与变量接口
- TelegramNotificationService 改为通过模板渲染发送（ORDER_SUCCESS/ORDER_FAILED/ORDER_FILTERED/CRYPTO_TAIL_SUCCESS/REDEEM_SUCCESS/REDEEM_NO_RETURN）
- 模板 CRUD、重置默认、测试发送接口
- 补全订单过滤相关 i18n key（zh/en/zh-TW）

前端:
- 消息推送设置抽离为独立页 /system-settings/notification
- 系统设置概览改为入口卡片，侧栏增加「消息推送设置」菜单
- NotificationSettingsPage: 机器人配置 + 模板配置双卡片布局（与概览一致）
- 模板配置支持选择类型、编辑内容、变量面板（点击复制、悬停说明）、保存/重置/测试
- 多语言 key 补全（notificationSettings.templates.*、templateTypes.*）

Made-with: Cursor

frontend/src/App.tsx

@@ -29,6 +29,7 @@ import CopyTradingSellOrders from './pages/CopyTradingSellOrders'
 import CopyTradingMatchedOrders from './pages/CopyTradingMatchedOrders'
 import FilteredOrdersList from './pages/FilteredOrdersList'
 import SystemSettings from './pages/SystemSettings'
+import NotificationSettingsPage from './pages/NotificationSettingsPage'
 import ApiHealthStatus from './pages/ApiHealthStatus'
 import RpcNodeSettings from './pages/RpcNodeSettings'
 import Announcements from './pages/Announcements'
@@ -268,6 +269,7 @@ function App() {
           <Route path="/users" element={<ProtectedRoute><UserList /></ProtectedRoute>} />
           <Route path="/announcements" element={<ProtectedRoute><Announcements /></ProtectedRoute>} />
           <Route path="/system-settings" element={<ProtectedRoute><SystemSettings /></ProtectedRoute>} />
+          <Route path="/system-settings/notification" element={<ProtectedRoute><NotificationSettingsPage /></ProtectedRoute>} />
           <Route path="/system-settings/rpc-nodes" element={<ProtectedRoute><RpcNodeSettings /></ProtectedRoute>} />          <Route path="/system-settings/api-health" element={<ProtectedRoute><ApiHealthStatus /></ProtectedRoute>} />
           
           {/* 默认重定向到登录页 */}