feat(storage): add audit persistence

backend/internal/audit/record.go

@@ -0,0 +1,26 @@
+package audit
+
+import "time"
+
+type Status string
+
+const (
+	StatusSuccess             Status = "success"
+	StatusValidationFailed    Status = "validation_failed"
+	StatusAuthenticationError Status = "authentication_error"
+	StatusUpstreamRejected    Status = "upstream_rejected"
+	StatusUpstreamTimeout     Status = "upstream_timeout"
+	StatusUpstreamUnavailable Status = "upstream_unavailable"
+	StatusInternalError       Status = "internal_error"
+)
+
+type Record struct {
+	RequestID          string
+	CreatedAt          time.Time
+	Duration           time.Duration
+	ClientIP           *string
+	Status             Status
+	UpstreamHTTPStatus *int
+	MaskedCard         string
+	ResponseJSON       []byte
+}