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.mod

@@ -145,6 +145,7 @@ require (
 	git.sr.ht/~mariusor/go-xsd-duration v0.0.0-20220703122237-02e73435a078 // indirect
 	github.com/Azure/azure-sdk-for-go/sdk/internal v1.11.2 // indirect
 	github.com/DataDog/zstd v1.5.7 // indirect
+	github.com/Masterminds/semver/v3 v3.4.0 // indirect
 	github.com/Microsoft/go-winio v0.6.2 // indirect
 	github.com/RoaringBitmap/roaring/v2 v2.10.0 // indirect
 	github.com/STARRY-S/zip v0.2.3 // indirect