feat: showcase auth and dashboard blocks on landing page

[secrethacker548-pixel]

Summary

• add a static site/ landing page inspired by the existing Jinjalume visual language
• showcase Login, Signup, and Admin Dashboard UI blocks above the component catalog
• add mobile navigation, copy interaction, reduced-motion handling, and responsive previews
• add a GitHub Pages deployment workflow and landing smoke tests

Validation

• 15 Playwright tests passed locally, with the desktop-only mobile-menu case intentionally skipped
• 14 pytest tests passed
• Ruff passed
• Tailwind build passed
• static landing page server smoke tests passed

The repository Pages source must be set to GitHub Actions for the new workflow to publish site/.