feat(antigravity): 添加配额窗口显示功能

后端:
- 新增 AntigravityQuotaRefresher 定时刷新配额
- Client 添加 FetchAvailableModels 方法获取模型配额
- 配额数据存入 account.extra.quota 字段

前端:
- AccountUsageCell 支持显示 Antigravity 账户配额
- UsageProgressBar 新增 amber 颜色
- 显示 G3P/G3F/G3I/C4.5 四个配额进度条

backend/internal/service/wire.go

@@ -54,6 +54,18 @@ func ProvideTimingWheelService() *TimingWheelService {
 	return svc
 }
 
+// ProvideAntigravityQuotaRefresher creates and starts AntigravityQuotaRefresher
+func ProvideAntigravityQuotaRefresher(
+	accountRepo AccountRepository,
+	proxyRepo ProxyRepository,
+	oauthSvc *AntigravityOAuthService,
+	cfg *config.Config,
+) *AntigravityQuotaRefresher {
+	svc := NewAntigravityQuotaRefresher(accountRepo, proxyRepo, oauthSvc, cfg)
+	svc.Start()
+	return svc
+}
+
 // ProvideDeferredService creates and starts DeferredService
 func ProvideDeferredService(accountRepo AccountRepository, timingWheel *TimingWheelService) *DeferredService {
 	svc := NewDeferredService(accountRepo, timingWheel, 10*time.Second)
@@ -102,4 +114,5 @@ var ProviderSet = wire.NewSet(
 	ProvideTokenRefreshService,
 	ProvideTimingWheelService,
 	ProvideDeferredService,
+	ProvideAntigravityQuotaRefresher,
 )