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/views/NotSupportedView.vue

@@ -0,0 +1,101 @@
+<template>
+  <BaseViewTemplate>
+    <div class="sad-container">
+      <!-- Right side image -->
+      <img
+        class="sad-girl"
+        src="/assets/images/sad_girl.png"
+        alt="Sad girl illustration"
+      />
+
+      <div class="no-drag sad-text flex items-center">
+        <div class="flex flex-col gap-8 p-8 min-w-110">
+          <!-- Header -->
+          <h1 class="text-4xl font-bold text-red-500">
+            {{ $t('notSupported.title') }}
+          </h1>
+
+          <!-- Message -->
+          <div class="space-y-4">
+            <p class="text-xl">
+              {{ $t('notSupported.message') }}
+            </p>
+            <ul class="list-disc list-inside space-y-1 text-neutral-800">
+              <li>{{ $t('notSupported.supportedDevices.macos') }}</li>
+              <li>{{ $t('notSupported.supportedDevices.windows') }}</li>
+            </ul>
+          </div>
+
+          <!-- Actions -->
+          <div class="flex gap-4">
+            <Button
+              :label="$t('notSupported.learnMore')"
+              icon="pi pi-github"
+              severity="secondary"
+              @click="openDocs"
+            />
+            <Button
+              :label="$t('notSupported.reportIssue')"
+              icon="pi pi-flag"
+              severity="secondary"
+              @click="reportIssue"
+            />
+            <Button
+              v-tooltip="$t('notSupported.continueTooltip')"
+              :label="$t('notSupported.continue')"
+              icon="pi pi-arrow-right"
+              icon-pos="right"
+              severity="danger"
+              @click="continueToInstall"
+            />
+          </div>
+        </div>
+      </div>
+    </div>
+  </BaseViewTemplate>
+</template>
+
+<script setup lang="ts">
+import Button from 'primevue/button'
+import { useRouter } from 'vue-router'
+
+import BaseViewTemplate from '@/views/templates/BaseViewTemplate.vue'
+
+const openDocs = () => {
+  window.open(
+    'https://github.com/Comfy-Org/desktop#currently-supported-platforms',
+    '_blank'
+  )
+}
+
+const reportIssue = () => {
+  window.open('https://forum.comfy.org/c/v1-feedback/', '_blank')
+}
+
+const router = useRouter()
+const continueToInstall = async () => {
+  await router.push('/install')
+}
+</script>
+
+<style scoped>
+@reference '../assets/css/style.css';
+
+.sad-container {
+  @apply grid items-center justify-evenly;
+  grid-template-columns: 25rem 1fr;
+
+  & > * {
+    grid-row: 1;
+  }
+}
+
+.sad-text {
+  grid-column: 1/3;
+}
+
+.sad-girl {
+  grid-column: 2/3;
+  width: min(75vw, 100vh);
+}
+</style>