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.

scripts/collect-i18n-general.ts

@@ -1,12 +1,12 @@
 import * as fs from 'fs'
 
+import { DESKTOP_DIALOGS } from '../apps/desktop-ui/src/constants/desktopDialogs'
 import { comfyPageFixture as test } from '../browser_tests/fixtures/ComfyPage'
 import {
   formatCamelCase,
   normalizeI18nKey
 } from '../packages/shared-frontend-utils/src/formatUtil'
 import { CORE_MENU_COMMANDS } from '../src/constants/coreMenuCommands'
-import { DESKTOP_DIALOGS } from '../src/constants/desktopDialogs'
 import { SERVER_CONFIG_ITEMS } from '../src/constants/serverConfig'
 import type { FormItem, SettingParams } from '../src/platform/settings/types'
 import type { ComfyCommandImpl } from '../src/stores/commandStore'