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/components/builder/EmptyWorkflowDialogContent.vue

@@ -6,7 +6,7 @@
 
     <div class="flex flex-col gap-2">
       <p class="m-0 text-sm text-muted-foreground">
-        {{ $t('builderToolbar.emptyWorkflowExplanation') }}
+        {{ $t('linearMode.emptyWorkflowExplanation') }}
       </p>
       <p class="m-0 text-sm text-muted-foreground">
         {{ $t('builderToolbar.emptyWorkflowPrompt') }}
@@ -19,10 +19,10 @@
         size="lg"
         @click="$emit('backToWorkflow')"
       >
-        {{ $t('builderToolbar.backToWorkflow') }}
+        {{ $t('linearMode.backToWorkflow') }}
       </Button>
       <Button variant="secondary" size="lg" @click="$emit('loadTemplate')">
-        {{ $t('builderToolbar.loadTemplate') }}
+        {{ $t('linearMode.loadTemplate') }}
       </Button>
     </template>
   </BuilderDialog>