refactor(antigravity): 统一额度刷新机制与 Claude 一致

将 Antigravity 的额度刷新从后台定时刷新改为按需获取模式，与 Claude 统一：

- 删除 AntigravityQuotaRefresher 后台服务
- 新增 QuotaFetcher 接口和 AntigravityQuotaFetcher 实现
- 前端改为调用 usage API 获取额度，支持 loading/error 状态
- 统一使用内存缓存（10 分钟 TTL）

backend/cmd/server/wire_gen.go

@@ -90,7 +90,8 @@ func initializeApplication(buildInfo handler.BuildInfo) (*Application, error) {
 	geminiQuotaService := service.NewGeminiQuotaService(configConfig, settingRepository)
 	rateLimitService := service.NewRateLimitService(accountRepository, usageLogRepository, configConfig, geminiQuotaService)
 	claudeUsageFetcher := repository.NewClaudeUsageFetcher()
-	accountUsageService := service.NewAccountUsageService(accountRepository, usageLogRepository, claudeUsageFetcher, geminiQuotaService)
+	antigravityQuotaFetcher := service.NewAntigravityQuotaFetcher(proxyRepository)
+	accountUsageService := service.NewAccountUsageService(accountRepository, usageLogRepository, claudeUsageFetcher, geminiQuotaService, antigravityQuotaFetcher)
 	geminiTokenCache := repository.NewGeminiTokenCache(redisClient)
 	geminiTokenProvider := service.NewGeminiTokenProvider(accountRepository, geminiTokenCache, geminiOAuthService)
 	gatewayCache := repository.NewGatewayCache(redisClient)
@@ -145,8 +146,7 @@ func initializeApplication(buildInfo handler.BuildInfo) (*Application, error) {
 	engine := server.ProvideRouter(configConfig, handlers, jwtAuthMiddleware, adminAuthMiddleware, apiKeyAuthMiddleware, apiKeyService, subscriptionService)
 	httpServer := server.ProvideHTTPServer(configConfig, engine)
 	tokenRefreshService := service.ProvideTokenRefreshService(accountRepository, oAuthService, openAIOAuthService, geminiOAuthService, antigravityOAuthService, configConfig)
-	antigravityQuotaRefresher := service.ProvideAntigravityQuotaRefresher(accountRepository, proxyRepository, antigravityOAuthService, configConfig)
-	v := provideCleanup(client, redisClient, tokenRefreshService, pricingService, emailQueueService, billingCacheService, oAuthService, openAIOAuthService, geminiOAuthService, antigravityOAuthService, antigravityQuotaRefresher)
+	v := provideCleanup(client, redisClient, tokenRefreshService, pricingService, emailQueueService, billingCacheService, oAuthService, openAIOAuthService, geminiOAuthService, antigravityOAuthService)
 	application := &Application{
 		Server:  httpServer,
 		Cleanup: v,
@@ -179,7 +179,6 @@ func provideCleanup(
 	openaiOAuth *service.OpenAIOAuthService,
 	geminiOAuth *service.GeminiOAuthService,
 	antigravityOAuth *service.AntigravityOAuthService,
-	antigravityQuota *service.AntigravityQuotaRefresher,
 ) func() {
 	return func() {
 		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
@@ -221,10 +220,6 @@ func provideCleanup(
 				antigravityOAuth.Stop()
 				return nil
 			}},
-			{"AntigravityQuotaRefresher", func() error {
-				antigravityQuota.Stop()
-				return nil
-			}},
 			{"Redis", func() error {
 				return rdb.Close()
 			}},