feat(gateway): 增强 /v1/usage 端点返回完整用量统计

为 CC Switch 集成增强 /v1/usage 网关端点，在保持原有 4 字段
(isValid, planName, remaining, unit) 向后兼容的基础上，新增：

- usage 对象：今日/累计的请求数、token 用量、费用，以及 RPM/TPM
- subscription 对象（订阅模式）：日/周/月用量和限额、过期时间
- balance 字段（余额模式）：当前钱包余额

用量数据获取采用 best-effort 策略，失败不影响基础响应。

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/cmd/server/wire_gen.go

@@ -173,7 +173,7 @@ func initializeApplication(buildInfo handler.BuildInfo) (*Application, error) {
 	userAttributeService := service.NewUserAttributeService(userAttributeDefinitionRepository, userAttributeValueRepository)
 	userAttributeHandler := admin.NewUserAttributeHandler(userAttributeService)
 	adminHandlers := handler.ProvideAdminHandlers(dashboardHandler, adminUserHandler, groupHandler, accountHandler, adminAnnouncementHandler, oAuthHandler, openAIOAuthHandler, geminiOAuthHandler, antigravityOAuthHandler, proxyHandler, adminRedeemHandler, promoHandler, settingHandler, opsHandler, systemHandler, adminSubscriptionHandler, adminUsageHandler, userAttributeHandler)
-	gatewayHandler := handler.NewGatewayHandler(gatewayService, geminiMessagesCompatService, antigravityGatewayService, userService, concurrencyService, billingCacheService, configConfig)
+	gatewayHandler := handler.NewGatewayHandler(gatewayService, geminiMessagesCompatService, antigravityGatewayService, userService, concurrencyService, billingCacheService, usageService, configConfig)
 	openAIGatewayHandler := handler.NewOpenAIGatewayHandler(openAIGatewayService, concurrencyService, billingCacheService, configConfig)
 	handlerSettingHandler := handler.ProvideSettingHandler(settingService, buildInfo)
 	totpHandler := handler.NewTotpHandler(totpService)