[feat] implement dynamic imports for locale code splitting (#6076)

## Summary
- Implement dynamic imports for internationalization (i18n) locale files
to reduce initial bundle size
- Only load English locale eagerly as default/fallback, load other
locales on-demand
- Apply code splitting to both main ComfyUI frontend and desktop-ui
applications

## Technical Details
- **Before**: All locale files (main.json, nodeDefs.json, commands.json,
settings.json) for all 9 languages were bundled in the initial
JavaScript bundle
- **After**: Only English locale files are included in initial bundle,
other locales are loaded dynamically when needed
- Implemented `loadLocale()` function that uses dynamic imports with
`Promise.all()` for efficient parallel loading
- Added locale tracking with `loadedLocales` Set to prevent duplicate
loading
- Updated both `src/i18n.ts` and `apps/desktop-ui/src/i18n.ts` with
consistent implementation

## Bundle Size Impact
This change significantly reduces the initial bundle size by removing ~8
languages worth of JSON locale data from the main bundle. Locale files
are now loaded on-demand only when users switch languages.

## Implementation
- Uses dynamic imports: `import('./locales/[locale]/[file].json')`
- Maintains backward compatibility with existing locale switching
mechanism
- Graceful error handling for unsupported locales
- No breaking changes to the public API

## Test plan
- [x] Verify initial load only includes English locale
- [x] Test dynamic locale loading when switching languages in settings
- [x] Confirm fallback behavior for unsupported locales
- [x] Validate both web and desktop-ui applications work correctly

🤖 Generated with [Claude Code](https://claude.ai/code)

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6076-feat-implement-dynamic-imports-for-locale-code-splitting-28d6d73d36508189ae0ef060804a5cee)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Claude <noreply@anthropic.com>

src/views/GraphView.vue

@@ -45,7 +45,7 @@ import { useCoreCommands } from '@/composables/useCoreCommands'
 import { useErrorHandling } from '@/composables/useErrorHandling'
 import { useProgressFavicon } from '@/composables/useProgressFavicon'
 import { SERVER_CONFIG_ITEMS } from '@/constants/serverConfig'
-import { i18n } from '@/i18n'
+import { i18n, loadLocale } from '@/i18n'
 import { useSettingStore } from '@/platform/settings/settingStore'
 import { useFrontendVersionMismatchWarning } from '@/platform/updates/common/useFrontendVersionMismatchWarning'
 import { useVersionCompatibilityStore } from '@/platform/updates/common/versionCompatibilityStore'
@@ -145,10 +145,17 @@ watchEffect(() => {
   )
 })
 
-watchEffect(() => {
+watchEffect(async () => {
   const locale = settingStore.get('Comfy.Locale')
   if (locale) {
-    i18n.global.locale.value = locale as 'en' | 'zh' | 'ru' | 'ja'
+    // Load the locale dynamically if not already loaded
+    try {
+      await loadLocale(locale)
+      // Type assertion is safe here as loadLocale validates the locale exists
+      i18n.global.locale.value = locale as typeof i18n.global.locale.value
+    } catch (error) {
+      console.error(`Failed to switch to locale "${locale}":`, error)
+    }
   }
 })