feat(web): integrate web routes and OAuth redirect support
- Register web frontend routes in main server
- Add post-login redirect support to OAuth handlers
- Store redirect URL in cookie during OAuth flow for delete-account
- Validate redirects are relative paths to prevent open redirect attacks
- Update user routes registration to include auth middleware
- Fix test mocks for actor handlers and comment service
- Update go.mod dependencies
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>