feat: App mode empty graph handling (#9393)

## Summary

Adds handling for entering app mode with an empty graph prompting the
user to load a template as a starting point

## Changes

- **What**: 
- app mode handle empty workflows, disable builder button, show
different message
- fix fitView when switching from app mode to graph

## Review Focus

Moving the fitView since the canvas is hidden in app mode until after
the workflow is loaded and the mode has been switched back to graph, I
don't see how this could cause any issues but worth a closer eye

## Screenshots (if applicable)

<img width="1057" height="916" alt="image"
src="https://github.com/user-attachments/assets/2ffe2b6d-9ce1-4218-828a-b7bc336c365a"
/>

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9393-feat-App-mode-empty-graph-handling-3196d73d3650812cab0ce878109ed5c9)
by [Unito](https://www.unito.io)

src/locales/en/main.json

@@ -3037,13 +3037,15 @@
     "downloadAll": "Download All",
     "viewJob": "View Job",
     "enterNodeGraph": "Enter node graph",
+    "emptyWorkflowExplanation": "Your workflow is empty. You need some nodes first to start building an app.",
+    "backToWorkflow": "Back to workflow",
+    "loadTemplate": "Load a template",
     "welcome": {
       "title": "App Mode",
       "message": "A simplified view that hides the node graph so you can focus on creating.",
       "controls": "Your outputs appear at the bottom, your controls are on the right. Everything else stays out of the way.",
       "sharing": "Share your workflow as a simple tool anyone can use. Export it from the tab menu and when others open it, they'll see App Mode. No node graph knowledge needed.",
       "getStarted": "Click {runButton} to get started.",
-      "backToWorkflow": "Back to workflow",
       "buildApp": "Build app"
     },
     "appModeToolbar": {
@@ -3388,10 +3390,7 @@
     "defaultModeAppliedGraphPrompt": "Would you like to view the app still?",
     "viewApp": "View app",
     "emptyWorkflowTitle": "This workflow has no nodes",
-    "emptyWorkflowExplanation": "Your workflow is empty. You need some nodes first to start building an app.",
-    "emptyWorkflowPrompt": "Do you want to start with a template?",
-    "backToWorkflow": "Back to workflow",
-    "loadTemplate": "Load a template"
+    "emptyWorkflowPrompt": "Do you want to start with a template?"
   },
   "builderMenu": {
     "exitAppBuilder": "Exit app builder"