Release Notes Are Now Hosted Directly on helmapp.dev

Helm update release notes are now hosted directly on helmapp.dev instead of linking out to GitHub release pages.

What changed

• Release automation generates per-tag release-note HTML from CHANGELOG.md.
• Generated notes are published under updates/release-notes/<tag>.html.
• Sparkle releaseNotesLink entries now point to these hosted pages.

Why this helps

• More consistent presentation in updater windows.
• Better control over formatting and release-note continuity.
• Cleaner future path for website-integrated release communication.