feat: App mode saving rework (#9338)

## Summary

Change app mode changes to be written directly to the workflow on change
instead of requiring explicit save via builder.
Temporary: Adds `.app.json` file extension to app files for
identification since we don't currently have a way to identify them with
metadata
Removes app builder save dialog and replaces it with default mode
selection

## Changes

- **What**: 
- ensure all save locations handle app mode
- remove dirtyLinearData and flushing

- **Breaking**: 
- if people are relying on workflow names and are converting to/from app
mode in the same workflow, they will gain/lose the `.app` part of the
extension

## Screenshots (if applicable)

<img width="689" height="84" alt="image"
src="https://github.com/user-attachments/assets/335596ee-dce9-4e3a-a7b5-f0715c294e41"
/>

<img width="421" height="324" alt="image"
src="https://github.com/user-attachments/assets/ad3cd33c-e9f0-4c30-8874-d4507892fc6b"
/>

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9338-feat-App-mode-saving-rework-3176d73d3650813f9ae1f6c5a234da8c)
by [Unito](https://www.unito.io)

src/components/builder/useAppSetDefaultView.ts

@@ -0,0 +1,47 @@
+import { computed } from 'vue'
+
+import { useWorkflowStore } from '@/platform/workflow/management/stores/workflowStore'
+import { app } from '@/scripts/app'
+import { useDialogService } from '@/services/dialogService'
+import { useDialogStore } from '@/stores/dialogStore'
+
+import DefaultViewDialogContent from './DefaultViewDialogContent.vue'
+
+const DIALOG_KEY = 'builder-default-view'
+
+export function useAppSetDefaultView() {
+  const workflowStore = useWorkflowStore()
+  const dialogService = useDialogService()
+  const dialogStore = useDialogStore()
+
+  const settingView = computed(() => dialogStore.isDialogOpen(DIALOG_KEY))
+
+  function showDialog() {
+    dialogService.showLayoutDialog({
+      key: DIALOG_KEY,
+      component: DefaultViewDialogContent,
+      props: {
+        initialOpenAsApp: workflowStore.activeWorkflow?.initialMode !== 'graph',
+        onApply: handleApply,
+        onClose: closeDialog
+      }
+    })
+  }
+
+  function handleApply(openAsApp: boolean) {
+    const workflow = workflowStore.activeWorkflow
+    if (!workflow) return
+
+    workflow.initialMode = openAsApp ? 'app' : 'graph'
+    const extra = (app.rootGraph.extra ??= {})
+    extra.linearMode = openAsApp
+    workflow.changeTracker?.checkState()
+    closeDialog()
+  }
+
+  function closeDialog() {
+    dialogStore.closeDialog({ key: DIALOG_KEY })
+  }
+
+  return { settingView, showDialog }
+}