Refactor config package validation

internal/config/config.go

@@ -125,7 +125,6 @@ type JobConfig struct {
 	// Timeout limits the job execution time (e.g., "10m").
 	Timeout time.Duration `yaml:"timeout,omitempty"`
 	// UserId identifies the user that owns conversations created by this job.
-	// It is assigned by the service until jobs are stored in the database.
 	UserId string `yaml:"user_id,omitempty"`
 }
 
@@ -145,6 +144,9 @@ func (cfg JobConfig) Validate() error {
 	if cfg.Timeout < 0 {
 		return fmt.Errorf("invalid timeout %v: must not be negative", cfg.Timeout)
 	}
+	if cfg.UserId == "" {
+		return fmt.Errorf("missing user_id")
+	}
 
 	return nil
 }