feat: Add System Overview tab to User Management page (admin only)

- Add backend API endpoint /api/users/system-strategies for system-wide strategy data
- Query all strategies across all users with positions, PnL, trade stats
- Add summary statistics (total strategies, running count, total capital, total PnL/ROI)
- Support filtering by status (running/stopped) and search by strategy/symbol/user
- Add System Overview tab with summary cards and detailed strategy table
- Display user, strategy name, status, symbol, capital, PnL/ROI, positions, trades, indicator, exchange, timeframe, leverage
- Add i18n translations for zh-CN and en-US
- Lazy-load strategy data when tab is first accessed

quantdinger_vue/src/locales/lang/en-US.js

@@ -2561,6 +2561,36 @@ const locale = {
   'userManage.selectDate': 'Please select a date',
   'userManage.remark': 'Remark',
   'userManage.remarkPlaceholder': 'Optional remark',
+  'userManage.tabUsers': 'User Management',
+
+  // System Overview (Admin)
+  'systemOverview.tabTitle': 'System Overview',
+  'systemOverview.totalStrategies': 'Total Strategies',
+  'systemOverview.runningStrategies': 'Running',
+  'systemOverview.totalCapital': 'Total Capital',
+  'systemOverview.totalPnl': 'Total PnL',
+  'systemOverview.filterAll': 'All Status',
+  'systemOverview.filterRunning': 'Running',
+  'systemOverview.filterStopped': 'Stopped',
+  'systemOverview.searchPlaceholder': 'Search strategy/symbol/user',
+  'systemOverview.running': 'Running',
+  'systemOverview.stopped': 'Stopped',
+  'systemOverview.colUser': 'User',
+  'systemOverview.colStrategy': 'Strategy',
+  'systemOverview.colStatus': 'Status',
+  'systemOverview.colSymbol': 'Symbol',
+  'systemOverview.colCapital': 'Capital',
+  'systemOverview.colPnl': 'PnL / ROI',
+  'systemOverview.colPositions': 'Pos',
+  'systemOverview.colTrades': 'Trades',
+  'systemOverview.colIndicator': 'Indicator',
+  'systemOverview.colExchange': 'Exchange',
+  'systemOverview.colTimeframe': 'TF',
+  'systemOverview.colLeverage': 'Lev',
+  'systemOverview.colCreatedAt': 'Created',
+  'systemOverview.realized': 'Real',
+  'systemOverview.unrealized': 'Unreal',
+  'systemOverview.symbols': 'symbols',
 
   // Settings - Billing
   'settings.group.billing': 'Billing & Credits',

quantdinger_vue/src/locales/lang/zh-CN.js

@@ -2370,6 +2370,36 @@ const locale = {
   'userManage.selectDate': '请选择日期',
   'userManage.remark': '备注',
   'userManage.remarkPlaceholder': '可选备注',
+  'userManage.tabUsers': '用户管理',
+
+  // System Overview (Admin)
+  'systemOverview.tabTitle': '系统总览',
+  'systemOverview.totalStrategies': '策略总数',
+  'systemOverview.runningStrategies': '运行中',
+  'systemOverview.totalCapital': '总资金',
+  'systemOverview.totalPnl': '总盈亏',
+  'systemOverview.filterAll': '全部状态',
+  'systemOverview.filterRunning': '运行中',
+  'systemOverview.filterStopped': '已停止',
+  'systemOverview.searchPlaceholder': '搜索策略名/交易对/用户名',
+  'systemOverview.running': '运行中',
+  'systemOverview.stopped': '已停止',
+  'systemOverview.colUser': '用户',
+  'systemOverview.colStrategy': '策略名称',
+  'systemOverview.colStatus': '状态',
+  'systemOverview.colSymbol': '交易对',
+  'systemOverview.colCapital': '资金',
+  'systemOverview.colPnl': '盈亏 / ROI',
+  'systemOverview.colPositions': '持仓',
+  'systemOverview.colTrades': '交易次数',
+  'systemOverview.colIndicator': '指标',
+  'systemOverview.colExchange': '交易所',
+  'systemOverview.colTimeframe': '周期',
+  'systemOverview.colLeverage': '杠杆',
+  'systemOverview.colCreatedAt': '创建时间',
+  'systemOverview.realized': '已实现',
+  'systemOverview.unrealized': '未实现',
+  'systemOverview.symbols': '个交易对',
 
   // Settings - Billing
   'settings.group.billing': '计费配置',