Add title and logo to release notes

[juliasilge]

Summary

Addresses #10516 by adding a header to the release notes page with the Positron logo and version number

Release Notes

New Features

• Release notes now display a header with the Positron logo and version number for clearer identification (Improve release notes with a title or similar #10516)

Bug Fixes

• N/A

QA Notes

1. In a daily build, you can confirm this using the command Developer: Open Current File as Release Notes
2. Open a file that will be used for release notes such as https://github.com/posit-dev/positron-website/blob/main/release-notes/release.md
3. Verify the header appears at the top with the Positron "P" logo and title
4. Test in both light and dark themes

[github-actions]

E2E Tests 🚀
This PR will run tests tagged with: @:critical

^{readme  valid tags}