Move release version resolution from build-time (vite.config.ts) to
runtime (server function on Cloudflare Workers). The server function
fetches GitHub releases, filters out prereleases/drafts, and only
returns a version that has all required assets (Mac DMG, Linux AppImage,
Windows exe). Uses Cloudflare's cf.cacheEverything with a 60s TTL to
avoid hitting GitHub on every request.
This fixes a race condition where the website would deploy and show
download links for a new release before the desktop build assets were
actually uploaded, resulting in 404s for users.
