Centralized management of external links (#4471)

Update the desktop guide links to make them platform and locale-aware

Edited by Terry:
Refactor external link management by introducing a centralized
useExternalLink composable with automatic locale and platform detection
for documentation URLs.

- Created useExternalLink composable - A new centralized utility for
managing all external links
- Dynamic docs URL builder (buildDocsUrl) - Automatically constructs
docs.comfy.org URLs with:
  - Locale detection (Chinese vs English)
  - Platform detection (macOS vs Windows for desktop)
  - Flexible path construction with options

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-4471-Add-platform-and-locale-aware-desktop-guide-URL-2346d73d3650815ea4a4dd64be575bbe)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Terry Jia <terryjia88@gmail.com>

tests-ui/tests/composables/useCoreCommands.test.ts

@@ -1,11 +1,24 @@
 import { createPinia, setActivePinia } from 'pinia'
 import { beforeEach, describe, expect, it, vi } from 'vitest'
+import { ref } from 'vue'
 
 import { useCoreCommands } from '@/composables/useCoreCommands'
 import { useSettingStore } from '@/platform/settings/settingStore'
 import { api } from '@/scripts/api'
 import { app } from '@/scripts/app'
 
+// Mock vue-i18n for useExternalLink
+const mockLocale = ref('en')
+vi.mock('vue-i18n', async (importOriginal) => {
+  const actual = await importOriginal<typeof import('vue-i18n')>()
+  return {
+    ...actual,
+    useI18n: vi.fn(() => ({
+      locale: mockLocale
+    }))
+  }
+})
+
 vi.mock('@/scripts/app', () => {
   const mockGraphClear = vi.fn()
   const mockCanvas = { subgraph: undefined }