fix: pass notification settings from create form to service

HandleAppCreate was not reading docker_network, ntfy_topic, or
slack_webhook form values, so these fields were silently dropped
during app creation. The app_new.html template had the form fields,
and CreateAppInput/CreateApp already supported these fields, but the
handler never passed them through.

Also adds these values to the template re-render data so they are
preserved if a validation error occurs during creation.

internal/handlers/app.go

@@ -54,12 +54,18 @@ func (h *Handlers) HandleAppCreate() http.HandlerFunc { //nolint:funlen // valid
 		repoURL := request.FormValue("repo_url")
 		branch := request.FormValue("branch")
 		dockerfilePath := request.FormValue("dockerfile_path")
+		dockerNetwork := request.FormValue("docker_network")
+		ntfyTopic := request.FormValue("ntfy_topic")
+		slackWebhook := request.FormValue("slack_webhook")
 
 		data := h.addGlobals(map[string]any{
 			"Name":           name,
 			"RepoURL":        repoURL,
 			"Branch":         branch,
 			"DockerfilePath": dockerfilePath,
+			"DockerNetwork":  dockerNetwork,
+			"NtfyTopic":      ntfyTopic,
+			"SlackWebhook":   slackWebhook,
 		}, request)
 
 		if name == "" || repoURL == "" {
@@ -100,6 +106,9 @@ func (h *Handlers) HandleAppCreate() http.HandlerFunc { //nolint:funlen // valid
 				RepoURL:        repoURL,
 				Branch:         branch,
 				DockerfilePath: dockerfilePath,
+				DockerNetwork:  dockerNetwork,
+				NtfyTopic:      ntfyTopic,
+				SlackWebhook:   slackWebhook,
 			},
 		)
 		if createErr != nil {