fix: changelog page SSR not fetching releases on Cloudflare Workers

Internal fetch to /changelog.json during SSR fails silently on Cloudflare
Workers. Refactor to use SolidStart query() with 'use server' directive
to fetch directly from GitHub API during SSR.

- Extract shared release fetching logic to lib/changelog.ts
- Update changelog page to use the new changelog() query
- Simplify changelog.json.ts to use shared fetchReleases()
- Add error logging for debugging