Upgrade to Astro 6 + Vite 7 + Tailwind 4.2

[llbbl]

Summary

When Astro 6.0 reaches stable, perform a coordinated upgrade of the Vite ecosystem dependencies.

Packages to upgrade

• astro 5.x → 6.x (brings Vite 7 support)
• vite 6.x → 7.x
• @tailwindcss/vite 4.1.x → 4.2+
• tailwindcss 4.1.x → 4.2+

Post-upgrade checklist

• Remove the pnpm overrides for vite in package.json
• Update the "Vite Version Constraint" section in CLAUDE.md
• Run full test suite + build verification
• Test all themes and search functionality
• Verify Node.js version compatibility (Vite 7 requires Node 20.19+ or 22.12+)

Context

• Astro 5.x bundles Vite 6 and is incompatible with Vite 7
• @tailwindcss/vite 4.2+ pulls in Vite 7 as a peer dep, causing TS plugin type conflicts
• We currently pin Tailwind packages to 4.1.x and override Vite to ^6.4.1
• Astro 6 is in beta with Vite 7 support: Update Vite peer dependency to v7 withastro/astro#14362

Blocked by

Astro 6.0 stable release