feat(alerts): add traffic spike detection with configurable thresholds

Introduce traffic_spike alert type for monitoring system and per-master
traffic levels with configurable thresholds stored in database.

- Add AlertThresholdConfig model for persistent threshold configuration
- Implement GET/PUT /admin/alerts/thresholds endpoints for threshold management
- Add traffic spike detection in alert detector cron job:
  - Global QPS monitoring across all masters
  - Per-master RPM/TPM checks with minimum sample thresholds
  - Per-master RPD/TPD checks for daily limits
- Use warning severity at threshold, critical at 2x threshold
- Include metric metadata (value, threshold, window) in alert details
- Update API documentation with new endpoints and alert type

internal/model/alert.go

@@ -16,6 +16,7 @@ const (
 	AlertTypeKeyDisabled   AlertType = "key_disabled"
 	AlertTypeKeyExpired    AlertType = "key_expired"
 	AlertTypeProviderDown  AlertType = "provider_down"
+	AlertTypeTrafficSpike  AlertType = "traffic_spike"
 )
 
 // AlertSeverity defines the severity level of an alert

internal/model/alert_threshold.go

@@ -0,0 +1,46 @@
+package model
+
+import (
+	"time"
+
+	"gorm.io/gorm"
+)
+
+// AlertThresholdConfig stores configurable thresholds for traffic spike detection
+type AlertThresholdConfig struct {
+	ID        uint           `gorm:"primaryKey" json:"id"`
+	CreatedAt time.Time      `json:"created_at"`
+	UpdatedAt time.Time      `json:"updated_at"`
+	DeletedAt gorm.DeletedAt `gorm:"index" json:"-"`
+
+	// Global thresholds
+	GlobalQPS int64 `gorm:"not null;default:100" json:"global_qps"` // System-wide QPS threshold
+
+	// Per-master thresholds
+	MasterRPM int64 `gorm:"not null;default:20" json:"master_rpm"`          // Requests per minute threshold
+	MasterRPD int64 `gorm:"not null;default:1000" json:"master_rpd"`        // Requests per day threshold
+	MasterTPM int64 `gorm:"not null;default:10000000" json:"master_tpm"`    // Tokens per minute threshold
+	MasterTPD int64 `gorm:"not null;default:100000000" json:"master_tpd"`   // Tokens per day threshold
+
+	// Minimum sample thresholds for 1-minute window checks
+	MinRPMRequests1m int64 `gorm:"not null;default:10" json:"min_rpm_requests_1m"`      // Min requests in 1m to trigger RPM check
+	MinTPMTokens1m   int64 `gorm:"not null;default:1000000" json:"min_tpm_tokens_1m"`   // Min tokens in 1m to trigger TPM check
+}
+
+// DefaultAlertThresholdConfig returns the default threshold configuration
+func DefaultAlertThresholdConfig() AlertThresholdConfig {
+	return AlertThresholdConfig{
+		GlobalQPS:        100,
+		MasterRPM:        20,
+		MasterRPD:        1000,
+		MasterTPM:        10_000_000,
+		MasterTPD:        100_000_000,
+		MinRPMRequests1m: 10,
+		MinTPMTokens1m:   1_000_000,
+	}
+}
+
+// TableName returns the table name for AlertThresholdConfig
+func (AlertThresholdConfig) TableName() string {
+	return "alert_threshold_configs"
+}