Docs: Proper release notes

[jkcinouye]

Summary

Adds more thorough release notes.

Details

This PR is intended to serve as scaffolding for a more automated release note process. We are including in this different files for testing purposes. We are retaining our bespoke announcements/highlights section, but copying over our GitHub release notes.

In this PR, there is a 'latest','preview','nightly' page along with a larger complete changelog. We will assess the analytics at the end of December to determine whether the latest, preview, and nightly pages are useful - if they are not, we will likely retain only the index.md (announcements/highlights) and archive/changelog.

[github-actions[bot]]

Size Change: -2 B (0%)

Total Size: 21.5 MB

ℹ️ View Unchanged

Filename	Size	Change
./bundle/gemini.js	21.5 MB	-2 B (0%)
./bundle/sandbox-macos-permissive-closed.sb	1.03 kB	0 B
./bundle/sandbox-macos-permissive-open.sb	890 B	0 B
./bundle/sandbox-macos-permissive-proxied.sb	1.31 kB	0 B
./bundle/sandbox-macos-restrictive-closed.sb	3.29 kB	0 B
./bundle/sandbox-macos-restrictive-open.sb	3.36 kB	0 B
./bundle/sandbox-macos-restrictive-proxied.sb	3.56 kB	0 B

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