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/ui/ZoomPane.vue

@@ -24,7 +24,7 @@ function handleWheel(e: WheelEvent) {
 
 let dragging = false
 function handleDown(e: PointerEvent) {
-  if (e.button !== 0) return
+  if (e.button !== 0 && e.button !== 1) return
 
   const zoomPaneEl = zoomPane.value
   if (!zoomPaneEl) return