refactor: replace sync.Map credits state with AICredits rate limit key

Replace process-memory sync.Map + per-model runtime state with a single
"AICredits" key in model_rate_limits, making credits exhaustion fully
isomorphic with model-level rate limiting.

Scheduler: rate-limited accounts with overages enabled + credits available
are now scheduled instead of excluded.

Forwarding: when model is rate-limited + credits available, inject credits
proactively without waiting for a 429 round trip.

Storage: credits exhaustion stored as model_rate_limits["AICredits"] with
5h duration, reusing SetModelRateLimit/isRateLimitActiveForKey.

Frontend: show credits_active (yellow ⚡) when model rate-limited but
credits available, credits_exhausted (red) when AICredits key active.

Tests: add unit tests for shouldMarkCreditsExhausted, injectEnabledCreditTypes,
clearCreditsExhausted, and update existing overages tests.

backend/internal/service/admin_service.go

@@ -143,9 +143,10 @@ type CreateGroupInput struct {
 	// 无效请求兜底分组 ID（仅 anthropic 平台使用）
 	FallbackGroupIDOnInvalidRequest *int64
 	// 模型路由配置（仅 anthropic 平台使用）
-	ModelRouting        map[string][]int64
-	ModelRoutingEnabled bool // 是否启用模型路由
-	MCPXMLInject        *bool
+	ModelRouting             map[string][]int64
+	ModelRoutingEnabled      bool // 是否启用模型路由
+	MCPXMLInject             *bool
+	SimulateClaudeMaxEnabled *bool
 	// 支持的模型系列（仅 antigravity 平台使用）
 	SupportedModelScopes []string
 	// Sora 存储配额
@@ -182,9 +183,10 @@ type UpdateGroupInput struct {
 	// 无效请求兜底分组 ID（仅 anthropic 平台使用）
 	FallbackGroupIDOnInvalidRequest *int64
 	// 模型路由配置（仅 anthropic 平台使用）
-	ModelRouting        map[string][]int64
-	ModelRoutingEnabled *bool // 是否启用模型路由
-	MCPXMLInject        *bool
+	ModelRouting             map[string][]int64
+	ModelRoutingEnabled      *bool // 是否启用模型路由
+	MCPXMLInject             *bool
+	SimulateClaudeMaxEnabled *bool
 	// 支持的模型系列（仅 antigravity 平台使用）
 	SupportedModelScopes *[]string
 	// Sora 存储配额
@@ -368,6 +370,10 @@ type ProxyExitInfoProber interface {
 	ProbeProxy(ctx context.Context, proxyURL string) (*ProxyExitInfo, int64, error)
 }
 
+type groupExistenceBatchReader interface {
+	ExistsByIDs(ctx context.Context, ids []int64) (map[int64]bool, error)
+}
+
 type proxyQualityTarget struct {
 	Target          string
 	URL             string
@@ -445,10 +451,6 @@ type userGroupRateBatchReader interface {
 	GetByUserIDs(ctx context.Context, userIDs []int64) (map[int64]map[int64]float64, error)
 }
 
-type groupExistenceBatchReader interface {
-	ExistsByIDs(ctx context.Context, ids []int64) (map[int64]bool, error)
-}
-
 // NewAdminService creates a new AdminService
 func NewAdminService(
 	userRepo UserRepository,
@@ -868,6 +870,13 @@ func (s *adminServiceImpl) CreateGroup(ctx context.Context, input *CreateGroupIn
 	if input.MCPXMLInject != nil {
 		mcpXMLInject = *input.MCPXMLInject
 	}
+	simulateClaudeMaxEnabled := false
+	if input.SimulateClaudeMaxEnabled != nil {
+		if platform != PlatformAnthropic && *input.SimulateClaudeMaxEnabled {
+			return nil, fmt.Errorf("simulate_claude_max_enabled only supported for anthropic groups")
+		}
+		simulateClaudeMaxEnabled = *input.SimulateClaudeMaxEnabled
+	}
 
 	// 如果指定了复制账号的源分组，先获取账号 ID 列表
 	var accountIDsToCopy []int64
@@ -924,6 +933,7 @@ func (s *adminServiceImpl) CreateGroup(ctx context.Context, input *CreateGroupIn
 		FallbackGroupIDOnInvalidRequest: fallbackOnInvalidRequest,
 		ModelRouting:                    input.ModelRouting,
 		MCPXMLInject:                    mcpXMLInject,
+		SimulateClaudeMaxEnabled:        simulateClaudeMaxEnabled,
 		SupportedModelScopes:            input.SupportedModelScopes,
 		SoraStorageQuotaBytes:           input.SoraStorageQuotaBytes,
 		AllowMessagesDispatch:           input.AllowMessagesDispatch,
@@ -1130,6 +1140,15 @@ func (s *adminServiceImpl) UpdateGroup(ctx context.Context, id int64, input *Upd
 	if input.MCPXMLInject != nil {
 		group.MCPXMLInject = *input.MCPXMLInject
 	}
+	if input.SimulateClaudeMaxEnabled != nil {
+		if group.Platform != PlatformAnthropic && *input.SimulateClaudeMaxEnabled {
+			return nil, fmt.Errorf("simulate_claude_max_enabled only supported for anthropic groups")
+		}
+		group.SimulateClaudeMaxEnabled = *input.SimulateClaudeMaxEnabled
+	}
+	if group.Platform != PlatformAnthropic {
+		group.SimulateClaudeMaxEnabled = false
+	}
 
 	// 支持的模型系列（仅 antigravity 平台使用）
 	if input.SupportedModelScopes != nil {
@@ -1530,7 +1549,7 @@ func (s *adminServiceImpl) UpdateAccount(ctx context.Context, id int64, input *U
 	if len(input.Credentials) > 0 {
 		account.Credentials = input.Credentials
 	}
-	if input.Extra != nil {
+	if len(input.Extra) > 0 {
 		// 保留配额用量字段，防止编辑账号时意外重置
 		for _, key := range []string{"quota_used", "quota_daily_used", "quota_daily_start", "quota_weekly_used", "quota_weekly_start"} {
 			if v, ok := account.Extra[key]; ok {
@@ -1539,11 +1558,15 @@ func (s *adminServiceImpl) UpdateAccount(ctx context.Context, id int64, input *U
 		}
 		account.Extra = input.Extra
 		if account.Platform == PlatformAntigravity && wasOveragesEnabled && !account.IsOveragesEnabled() {
-			delete(account.Extra, antigravityCreditsOveragesKey)
+			delete(account.Extra, "antigravity_credits_overages") // 清理旧版 overages 运行态
+			// 清除 AICredits 限流 key
+			if rawLimits, ok := account.Extra[modelRateLimitsKey].(map[string]any); ok {
+				delete(rawLimits, creditsExhaustedKey)
+			}
 		}
 		if account.Platform == PlatformAntigravity && !wasOveragesEnabled && account.IsOveragesEnabled() {
 			delete(account.Extra, modelRateLimitsKey)
-			delete(account.Extra, antigravityCreditsOveragesKey)
+			delete(account.Extra, "antigravity_credits_overages") // 清理旧版 overages 运行态
 		}
 		// 校验并预计算固定时间重置的下次重置时间
 		if err := ValidateQuotaResetConfig(account.Extra); err != nil {
@@ -1627,14 +1650,6 @@ func (s *adminServiceImpl) UpdateAccount(ctx context.Context, id int64, input *U
 	if err := s.accountRepo.Update(ctx, account); err != nil {
 		return nil, err
 	}
-	if account.Platform == PlatformAntigravity {
-		if !account.IsOveragesEnabled() && wasOveragesEnabled {
-			clearCreditsExhausted(account.ID)
-		}
-		if account.IsOveragesEnabled() && !wasOveragesEnabled {
-			clearCreditsExhausted(account.ID)
-		}
-	}
 
 	// 绑定分组
 	if input.GroupIDs != nil {