feat: add AI chat for repports

backend/internal/models/models.go

@@ -116,3 +116,12 @@ type Report struct {
 	ErrorMsg       string    `json:"error_msg"`
 	CreatedAt      time.Time `json:"created_at"`
 }
+
+type ReportMessage struct {
+	ID        string    `json:"id"`
+	ReportID  string    `json:"report_id"`
+	Role      string    `json:"role"` // user | assistant
+	Content   string    `json:"content"`
+	Status    string    `json:"status"` // done | generating | error
+	CreatedAt time.Time `json:"created_at"`
+}