Update Astro and transitive package dependencies

[colmarius]

Updates Astro from 7.2.0 to 7.3.5 and refreshes compatible transitive dependencies.

Verification:

• npm ci succeeds
• npm audit: zero vulnerabilities
• npm outdated: no outdated direct dependencies
• ./scripts/test.sh: lint and all 112 Bats tests pass
• npm run build succeeds
• Browser smoke check: homepage renders, Docs navigation works, documentation has no horizontal overflow at desktop and narrow widths, no browser errors