fix: App mode - Widget dropdowns clipped in sidebar (#10338)

## Summary

Popover components for graph mode are appendTo self so scale/translate
works, however in the sidebar this causes them to be clipped by the
parent overflow. This adds a provide/inject flag to change these to be
appended to the body.

## Changes

- **What**: 
- add append to injection for overriding where popovers are mounted
- ensure dropdowns respect this flag
- extract enterAppModeWithInputs helper
- tests

Before:  
<img width="225" height="140" alt="image"
src="https://github.com/user-attachments/assets/bd83b0cd-49a9-45dd-8344-4c10221444fc"
/>

After:  
<img width="238" height="225" alt="image"
src="https://github.com/user-attachments/assets/286e28e9-b37d-4ffc-91a9-7c340757d3fc"
/>

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-10338-fix-App-mode-Widget-dropdowns-clipped-in-sidebar-3296d73d365081e2ba38e3e82006d65e)
by [Unito](https://www.unito.io)

src/composables/useTransformCompatOverlayProps.ts

@@ -1,5 +1,6 @@
 import type { HintedString } from '@primevue/core'
-import { computed } from 'vue'
+import type { InjectionKey } from 'vue'
+import { computed, inject } from 'vue'
 
 /**
  * Options for configuring transform-compatible overlay props
@@ -15,6 +16,10 @@ interface TransformCompatOverlayOptions {
   // autoZIndex?: boolean
 }
 
+export const OverlayAppendToKey: InjectionKey<
+  HintedString<'body' | 'self'> | undefined | HTMLElement
+> = Symbol('OverlayAppendTo')
+
 /**
  * Composable that provides props to make PrimeVue overlay components
  * compatible with CSS-transformed parent elements.
@@ -41,8 +46,10 @@ interface TransformCompatOverlayOptions {
 export function useTransformCompatOverlayProps(
   overrides: TransformCompatOverlayOptions = {}
 ) {
+  const injectedAppendTo = inject(OverlayAppendToKey, undefined)
+
   return computed(() => ({
-    appendTo: 'self' as const,
+    appendTo: injectedAppendTo ?? ('self' as const),
     ...overrides
   }))
 }