feat: rewrite with Starlight

[zlataovce]

This is a rewrite using the Starlight documentation generator instead of Docusaurus. The goal is to standardize the framework choice and look with our website (pending rewrite in Astro), improve performance, editing experience and maintainability (dropping Docusaurus hack-patches).

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TODO:

• [ ] TODOs in code
• [ ] Components
  • [x] Javadoc - replaced with custom Markdown links (using a remark plugin)
  • [x] SoftwareVersion - replaced with MDX import+constant replacement
  • [x] Property - replaced with MDX import+constant replacement or removed altogether
  • [x] VersionFormattedCode - replaced with a remark plugin (constants defined in astro.config.ts)
  • [ ] Configuration-related components
• [ ] Pages
  • [x] /paper/admin
    • [ ] Configuration reference
    • [x] Permissions reference
  • [x] /paper/dev
    • [ ] API pages
  • [x] /paper/contributing
  • [x] /folia/admin
  • [x] /velocity/admin
  • [x] /velocity/dev
    • [ ] Component API (passthrough to the Paper pages)
  • [x] /waterfall
    • [ ] Configuration
  • [x] /misc
    • [ ] Start script generator
    • [ ] Item command converter
  • [x] Create index.md(x) for each subdirectory - Docusaurus generates index pages, Starlight does not
• [ ] Drop Starlight patch in favor of https://github.com/withastro/starlight/pull/3024
• [ ] Rewrite all links to absolute ones and enable link validator
• [x] Revise theme colors
• [x] Add mermaid diagram support (replaced with D2)
• [ ] Rename .mdx -> .md where no MDX features are used
  • [ ] Re-enable Prettier for .md files

Blocked on:

• https://github.com/withastro/starlight/pull/3033
• https://github.com/withastro/starlight/pull/3024

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[kashike]

I have no issues with us migrating to Starlight - this looks good so far.

[zlataovce]

this is now mergeable (ready for review), as Starlight has merged and released the last needed feature

(project icons are currently patched in and should be replaced with https://github.com/withastro/starlight/pull/3024, but the patch can be dropped whenever, not a blocker)

[EterNityCH]

This is epic 🔥