Even further app fixes (#9617)

- Allow dragging zoom pane with middle click
- Prevent selection of canvasOnly widgets
- These widgets would not display in app mode, so allow selection would
only cause confusion.
- Support displaying the error dialogue in app mode
- Add a somewhat involved mobile app mode error indication system
<img width="300" alt="image"
src="https://github.com/user-attachments/assets/d8793bbd-fff5-4b2a-a316-6ff154bae2c4"
/> <img width="300" alt="image"
src="https://github.com/user-attachments/assets/cb88b0f6-f7e5-409e-ae43-f1348f946b19"
/>

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9617-Even-further-app-fixes-31d6d73d365081c891dfdfe3477cfd61)
by [Unito](https://www.unito.io)

src/components/builder/AppBuilder.vue

@@ -160,7 +160,7 @@ function handleClick(e: MouseEvent) {
     else appModeStore.selectedOutputs.splice(index, 1)
     return
   }
-  if (!isSelectInputsMode.value) return
+  if (!isSelectInputsMode.value || widget.options.canvasOnly) return
 
   const index = appModeStore.selectedInputs.findIndex(
     ([nodeId, widgetName]) => node.id == nodeId && widget.name === widgetName