Summary:
The `facebook` GitHub org was renamed to `meta` (https://fb.workplace.com/groups/metaopensource/permalink/29110262721924097/), and a new, empty `facebook` org took the old name. GitHub Pages does not redirect after an org rename, so https://facebook.github.io/memlab/ now 404s ("There isn't a GitHub Pages site here"). The site is served at https://meta.github.io/memlab/.

This moves every memlab link to the new org:
- `website/docusaurus.config.js`: `url` is now `https://meta.github.io/` and `organizationName` is `meta`, so canonical URLs, the sitemap and edit links match where the site is served. `baseUrl` stays `/memlab/`.
- `facebook.github.io/memlab` and `github.com/facebook/memlab` (including `git@github.com:facebook/memlab.git`) become `meta.github.io/memlab` and `github.com/meta/memlab` in the READMEs, `AI.md`, the docs, the search index config, the homepage, and the `homepage`/`repository`/`bugs` fields of every package `package.json`.

Links to other projects (for example `github.com/facebook/react`) are unchanged. The npm package pages keep the old links until the next release.

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landed-with-radar-review

Differential Revision: D128198143

fbshipit-source-id: a5d111054843a48095eb5de2b7a3af92f8d4b7c5