feat(admin): 新增账户余额/配额查询与展示

- 新增 accountBalanceService 与多 Provider 适配（Claude/Claude Console/OpenAI Responses/通用）
  - Redis 增加余额查询结果与本地统计缓存读写
  - 管理端新增 /admin/accounts/balance 相关接口与汇总接口，并在应用启动时注册 Provider
  - 后台前端新增余额组件与 Dashboard 余额/配额汇总、低余额/高使用提示
  - 补充 accountBalanceService 单元测试

src/routes/admin/index.js

@@ -21,6 +21,7 @@ const openaiResponsesAccountsRoutes = require('./openaiResponsesAccounts')
 const droidAccountsRoutes = require('./droidAccounts')
 const dashboardRoutes = require('./dashboard')
 const usageStatsRoutes = require('./usageStats')
+const accountBalanceRoutes = require('./accountBalance')
 const systemRoutes = require('./system')
 const concurrencyRoutes = require('./concurrency')
 const claudeRelayConfigRoutes = require('./claudeRelayConfig')
@@ -36,6 +37,7 @@ router.use('/', openaiResponsesAccountsRoutes)
 router.use('/', droidAccountsRoutes)
 router.use('/', dashboardRoutes)
 router.use('/', usageStatsRoutes)
+router.use('/', accountBalanceRoutes)
 router.use('/', systemRoutes)
 router.use('/', concurrencyRoutes)
 router.use('/', claudeRelayConfigRoutes)