feat(gateway): 账户切换次数和 Antigravity 限流时间可配置

- gateway.max_account_switches: 账户切换最大次数，默认 10
- gateway.max_account_switches_gemini: Gemini 账户切换次数，默认 3
- gateway.antigravity_fallback_cooldown_minutes: Antigravity 429 fallback 限流时间，默认 5 分钟
- Antigravity 429 不再重试，直接标记账户限流

backend/internal/handler/gateway_handler.go

@@ -30,6 +30,8 @@ type GatewayHandler struct {
 	userService               *service.UserService
 	billingCacheService       *service.BillingCacheService
 	concurrencyHelper         *ConcurrencyHelper
+	maxAccountSwitches        int
+	maxAccountSwitchesGemini  int
 }
 
 // NewGatewayHandler creates a new GatewayHandler
@@ -43,8 +45,16 @@ func NewGatewayHandler(
 	cfg *config.Config,
 ) *GatewayHandler {
 	pingInterval := time.Duration(0)
+	maxAccountSwitches := 10
+	maxAccountSwitchesGemini := 3
 	if cfg != nil {
 		pingInterval = time.Duration(cfg.Concurrency.PingInterval) * time.Second
+		if cfg.Gateway.MaxAccountSwitches > 0 {
+			maxAccountSwitches = cfg.Gateway.MaxAccountSwitches
+		}
+		if cfg.Gateway.MaxAccountSwitchesGemini > 0 {
+			maxAccountSwitchesGemini = cfg.Gateway.MaxAccountSwitchesGemini
+		}
 	}
 	return &GatewayHandler{
 		gatewayService:            gatewayService,
@@ -53,6 +63,8 @@ func NewGatewayHandler(
 		userService:               userService,
 		billingCacheService:       billingCacheService,
 		concurrencyHelper:         NewConcurrencyHelper(concurrencyService, SSEPingFormatClaude, pingInterval),
+		maxAccountSwitches:        maxAccountSwitches,
+		maxAccountSwitchesGemini:  maxAccountSwitchesGemini,
 	}
 }
 
@@ -164,7 +176,7 @@ func (h *GatewayHandler) Messages(c *gin.Context) {
 	}
 
 	if platform == service.PlatformGemini {
-		const maxAccountSwitches = 3
+		maxAccountSwitches := h.maxAccountSwitchesGemini
 		switchCount := 0
 		failedAccountIDs := make(map[int64]struct{})
 		lastFailoverStatus := 0
@@ -291,7 +303,7 @@ func (h *GatewayHandler) Messages(c *gin.Context) {
 		}
 	}
 
-	const maxAccountSwitches = 10
+	maxAccountSwitches := h.maxAccountSwitches
 	switchCount := 0
 	failedAccountIDs := make(map[int64]struct{})
 	lastFailoverStatus := 0

backend/internal/handler/gemini_v1beta_handler.go

@@ -212,7 +212,7 @@ func (h *GatewayHandler) GeminiV1BetaModels(c *gin.Context) {
 	if sessionHash != "" {
 		sessionKey = "gemini:" + sessionHash
 	}
-	const maxAccountSwitches = 3
+	maxAccountSwitches := h.maxAccountSwitchesGemini
 	switchCount := 0
 	failedAccountIDs := make(map[int64]struct{})
 	lastFailoverStatus := 0

backend/internal/handler/openai_gateway_handler.go

@@ -23,6 +23,7 @@ type OpenAIGatewayHandler struct {
 	gatewayService      *service.OpenAIGatewayService
 	billingCacheService *service.BillingCacheService
 	concurrencyHelper   *ConcurrencyHelper
+	maxAccountSwitches  int
 }
 
 // NewOpenAIGatewayHandler creates a new OpenAIGatewayHandler
@@ -33,13 +34,18 @@ func NewOpenAIGatewayHandler(
 	cfg *config.Config,
 ) *OpenAIGatewayHandler {
 	pingInterval := time.Duration(0)
+	maxAccountSwitches := 3
 	if cfg != nil {
 		pingInterval = time.Duration(cfg.Concurrency.PingInterval) * time.Second
+		if cfg.Gateway.MaxAccountSwitches > 0 {
+			maxAccountSwitches = cfg.Gateway.MaxAccountSwitches
+		}
 	}
 	return &OpenAIGatewayHandler{
 		gatewayService:      gatewayService,
 		billingCacheService: billingCacheService,
 		concurrencyHelper:   NewConcurrencyHelper(concurrencyService, SSEPingFormatComment, pingInterval),
+		maxAccountSwitches:  maxAccountSwitches,
 	}
 }
 
@@ -147,7 +153,7 @@ func (h *OpenAIGatewayHandler) Responses(c *gin.Context) {
 	// Generate session hash (from header for OpenAI)
 	sessionHash := h.gatewayService.GenerateSessionHash(c)
 
-	const maxAccountSwitches = 3
+	maxAccountSwitches := h.maxAccountSwitches
 	switchCount := 0
 	failedAccountIDs := make(map[int64]struct{})
 	lastFailoverStatus := 0