Introduces a new feature to fetch, parse, and display app release notes
and update highlights directly within the UI.
- Backend: Adds the `release-notes` module to fetch GitHub releases
and parse markdown highlight sections.
- Frontend: Adds the `WhatsNew` dialog and view, including custom
markdown rendering and an image lightbox for update media.
- Tools: Adds validation scripts (`whats-new-lint`, `whats-new-preview`)
to ensure release content parses correctly before publication.
neon