feat: upgrade Dyne.org to Astro 7

[jaromil]

Summary

• upgrade the static site through Astro 6/Vite 7/Tailwind 4 to Astro 7.2.6/Vite 8.2.2
• migrate the deprecated Tailwind integration to the Tailwind 4 Vite plugin
• remove temporary audit exceptions; the current audit reports zero high/critical vulnerabilities
• document clean-room verification, GitHub Pages artifact checks, and non-destructive rollback boundaries

Verification

• npm test: 34/34
• npm run test:e2e: 80 passed, 2 expected skips
• clean online/offline builds: 77 routes
• npm audit --audit-level=high: zero high/critical findings

The local .gestalt Org plan remains intentionally untracked.