Decouple Desktop UI into monorepo app (#5912)

## Summary

Extracts desktop UI into apps/desktop-ui package with minimal changes.

## Changes

- **What**:
- Separates desktop-specific code into standalone package with
independent Vite config, router, and i18n
- Drastically simplifies the main app router by removing all desktop
routes
  - Adds a some code duplication, most due to the existing design
- Some duplication can be refactored to be *simpler* on either side - no
need to split things by `isElectron()`
  - Rudimentary storybook support has been added
- **Breaking**: Stacked PR for publishing must be merged before this PR
makes it to stable core (but publishing _could_ be done manually)
  - #5915
- **Dependencies**: Takes full advantage of pnpm catalog. No additional
dependencies added.

## Review Focus

- Should be no changes to normal frontend operation
- Scripts added to root package.json are acceptable
- The duplication in this PR is copied as is, wherever possible. Any
corrections or fix-ups beyond the scope of simply migrating the
functionality as-is, can be addressed in later PRs. That said, if any
changes are made, it instantly becomes more difficult to separate the
duplicated code out into a shared utility.
  - Tracking issue to address concerns: #5925

### i18n

Fixing i18n is out of scope for this PR. It is a larger task that we
should consider carefully and implement properly. Attempting to isolate
the desktop i18n and duplicate the _current_ localisation scripts would
be wasted energy.

src/utils/refUtil.ts

@@ -1,29 +0,0 @@
-import { useTimeout } from '@vueuse/core'
-import { type Ref, computed, ref, watch } from 'vue'
-
-/**
- * Vue boolean ref (writable computed) with one difference: when set to `true` it stays that way for at least {@link minDuration}.
- * If set to `false` before {@link minDuration} has passed, it uses a timer to delay the change.
- * @param value The default value to set on this ref
- * @param minDuration The minimum time that this ref must be `true` for
- * @returns A custom boolean vue ref with a minimum activation time
- */
-export function useMinLoadingDurationRef(
-  value: Ref<boolean>,
-  minDuration = 250
-) {
-  const current = ref(value.value)
-
-  const { ready, start } = useTimeout(minDuration, {
-    controls: true,
-    immediate: false
-  })
-
-  watch(value, (newValue) => {
-    if (newValue && !current.value) start()
-
-    current.value = newValue
-  })
-
-  return computed(() => current.value || !ready.value)
-}