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.

apps/desktop-ui/src/components/maintenance/TaskListStatusIcon.vue

@@ -0,0 +1,45 @@
+<template>
+  <ProgressSpinner v-if="!state || loading" class="h-8 w-8" />
+  <template v-else>
+    <i v-tooltip.top="{ value: tooltip, showDelay: 250 }" :class="cssClasses" />
+  </template>
+</template>
+
+<script setup lang="ts">
+import { PrimeIcons } from '@primevue/core/api'
+import ProgressSpinner from 'primevue/progressspinner'
+import type { MaybeRef } from 'vue'
+import { computed } from 'vue'
+
+import { t } from '@/i18n'
+
+// Properties
+const tooltip = computed(() => {
+  if (props.state === 'error') {
+    return t('g.error')
+  } else if (props.state === 'OK') {
+    return t('maintenance.OK')
+  } else {
+    return t('maintenance.Skipped')
+  }
+})
+
+const cssClasses = computed(() => {
+  let classes: string
+  if (props.state === 'error') {
+    classes = `${PrimeIcons.EXCLAMATION_TRIANGLE} text-red-500`
+  } else if (props.state === 'OK') {
+    classes = `${PrimeIcons.CHECK} text-green-500`
+  } else {
+    classes = PrimeIcons.MINUS
+  }
+
+  return `text-3xl pi ${classes}`
+})
+
+// Model
+const props = defineProps<{
+  state: 'warning' | 'error' | 'resolved' | 'OK' | 'skipped' | undefined
+  loading?: MaybeRef<boolean>
+}>()
+</script>