feat(alerts): add MasterID to log records and improve traffic spike detection

- Add MasterID field with index to LogRecord model for efficient queries
- Fix threshold config loading to use fixed ID=1 with FirstOrCreate
- Allow traffic spike detection to work without Redis for log-based checks
- Add traffic_spike to API documentation for alert type filter
- Add comprehensive tests for RPM/RPD/TPM spike detection scenarios

internal/model/log.go

@@ -6,6 +6,7 @@ import "gorm.io/gorm"
 type LogRecord struct {
 	gorm.Model
 	Group        string `json:"group"`
+	MasterID     uint   `gorm:"index" json:"master_id"`
 	KeyID        uint   `json:"key_id"`
 	ModelName    string `json:"model"`
 	ProviderID   uint   `json:"provider_id"`