fix: fail app on empty app url before parsing

internal/bootstrap/app_bootstrap.go

@@ -47,6 +47,10 @@ func (app *BootstrapApp) Setup() error {
 	fmt.Println("Tinyauth is moving to an organization! All versions after v5.0.7 will be released under ghcr.io/tinyauthapp/tinyauth. Existing images will continue to work but new features and updates (including security ones) will only be released under the new image path.")
 
 	// get app url
+	if app.config.AppURL == "" {
+		return fmt.Errorf("app URL cannot be empty, perhaps config loading failed")
+	}
+
 	appUrl, err := url.Parse(app.config.AppURL)
 
 	if err != nil {