feat: Show empty workflow dialog when entering app builder with no nodes (#9379)

## Summary

Prompts users to load a template or return to graph when entering
builder mode on an empty workflow

## Screenshots (if applicable)

<img width="627" height="275" alt="image"
src="https://github.com/user-attachments/assets/c1a35dc3-4e8f-4abd-95b9-2f92524e8ebf"
/>

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9379-feat-Show-empty-workflow-dialog-when-entering-app-builder-with-no-nodes-3196d73d36508123b643ec893cd86cac)
by [Unito](https://www.unito.io)

src/locales/en/main.json

@@ -2593,7 +2593,7 @@
     "duplicate": "Duplicate",
     "enterAppMode": "Enter app mode",
     "exitAppMode": "Exit app mode",
-    "enterBuilderMode": "Enter app builder",
+    "enterBuilderMode": "App builder",
     "workflowActions": "Workflow actions",
     "clearWorkflow": "Clear Workflow",
     "deleteWorkflow": "Delete Workflow",
@@ -3379,7 +3379,12 @@
     "defaultModeAppliedAppPrompt": "Would you like to view it now?",
     "defaultModeAppliedGraphBody": "This workflow will open as a node graph by default from now on.",
     "defaultModeAppliedGraphPrompt": "Would you like to view the app still?",
-    "viewApp": "View app"
+    "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"
   },
   "builderMenu": {
     "exitAppBuilder": "Exit app builder"