Migrate to Astro

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For more configurability and extensibility, we'll switch to Astro.

• [x] Migrate to Astro-flavoured markdown
• [x] Add brand customization (logo, type, colors)
• [x] Register Fission app: everywhere-computer-docs.fission.app
• [x] Add opengraph support
• [x] Setup publishing pipeline to Fission CLI
• [x] Redirect docs.everywhere.computer
• [x] Preliminary investigation into i18n
• [x] Preliminary investigation into versioning support

[depatchedmode]

Just a quick couple of notes:

1. i18n is baked into the Starlight theme that we are using. Docs can be found at http://starlight.astro.build. TLDR: is a separate directory for each language code. So, it's supported.
2. Versioning has been discussed at length in the community, and there may soon be a canonical solution. The recommended approach is to branch for versions, so that clean up and small fixes can still be made. This still requires an approach. A few resources:
   • Good thread on approaches and current progress: https://github.com/withastro/starlight/discussions/957
   • Recently posted Vercel + Astro recipe: https://www.webpro.nl/scraps/versioned-docs-with-starlight-and-vercel
   • Ongoing Discord thread: https://discord.com/channels/830184174198718474/1117052663520034866

[depatchedmode]

@walkah Would you mind pointing docs.everywhere.computer at everywhere-computer-docs.fission.app when you have a moment?