showcase(vibe-kanban): Added Google SSO Authentication for security purposes

[willypt]

Thanks for pioneering Vibe Kanban! The product is truly well made—I'm currently looking to host it on a dedicated machine so non-engineering teams can use VK for their day-to-day work.

One thing I noticed is missing: protection for the directory and tasks, especially during initial login. I tried vibe-coding an addition to VK for Google SSO authentication, and the feature looks fine and feels right at home.

Would there be interest in an official approach to this?

Steps to Test:

• Fork the PR showcase(google-sso): Add simple google sso validation #1704
• Create Google API Credential
• Populate these environment variables during runtime

GOOGLE_SSO_ENABLED=true
GOOGLE_CLIENT_ID=xxxxxxxx-yyyyyyyyy.apps.googleusercontent.com
GOOGLE_ALLOWED_DOMAINS=gmail.com #optional

• Expect the screenshot below is shown
• Expect user can't access VK at all if they haven't been authenticated yet using Google SSO