feat(api): Add v2 API for public releases and app updates

- Add public_landing option to allow private repos to have public landing pages
- Add public_releases option to allow private repos to serve releases publicly
- Add /api/v2/repos/{owner}/{repo}/releases/update endpoint for Electron/Squirrel compatible app updates
- Add /api/v2/repos/{owner}/{repo}/pages/config and /content endpoints
- Add repoAssignmentWithPublicAccess middleware to bypass auth for public landing/releases
- Update README with documentation for new features

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

go.sum

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