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>
