fix(deps): update dependencies to latest stable versions

[jongio]

Summary

Updates all web dependencies in web/package.json to their latest stable versions.

Updated Packages

Dependencies

Package	Before	After
@astrojs/mdx	^4.3.13	^5.0.6
astro	^5.17.1	^6.3.3
astro-expressive-code	^0.41.6	^0.42.0

Dev Dependencies

Package	Before	After
@playwright/test	^1.58.1	^1.60.0
@tailwindcss/vite	^4.1.18	^4.3.0
@types/node	^25.2.1	^25.8.0
autoprefixer	^10.4.24	^10.5.0
postcss	^8.5.6	^8.5.14
tailwindcss	^4.1.18	^4.3.0
tsx	^4.21.0	^4.22.1
typescript	^5.9.3	^6.0.3

Testing

• CLI unit tests: passed
• Web (Playwright) chromium tests: 38 passed, 7 failed (all 7 failures are pre-existing on main branch and unrelated to this update)

Notable Changes

• astro and @astrojs/mdx: Major version bumps (5 to 6, 4 to 5). These are breaking-change releases. The site builds and tests pass identically to main.
• typescript: Major version bump (5 to 6).
• All other packages are minor or patch updates.