[codex] Set up monorepo foundation

[jderochervlk]

Context

This is the foundation PR for splitting the existing docs site into a monorepo before adding the separate interactive guide site. It keeps the current docs app behavior intact while moving it under apps/docs and making root scripts delegate to the docs workspace.

Summary

• Add a Yarn workspace root with apps/* and packages/*, and move the existing site package to apps/docs as @rescript-lang/docs.
• Move the docs app, source, content, scripts, tests, assets, functions, and config files under apps/docs with mostly pure renames.
• Update root scripts, Makefile, ignore/format config, generated-script paths, source/edit links, and deployment workflows for the new docs workspace location.
• Keep this PR limited to monorepo structure; it does not add guide content or a guide app yet.

Validation

• yarn build:res
• yarn ci:format
• yarn build:scripts
• yarn build:update-index
• yarn workspace @rescript-lang/docs ci:format
• yarn build
• git diff --check

Known test caveat

yarn test does not complete in this checkout. It timed out during the MDX example/compiler path, and the isolated generated temp project repro also timed out with rescript build apps/docs/temp --quiet. The docs href test itself exits 0, with the existing link warnings. This appears to be separate from the monorepo production build path, which exits 0.

[github-actions]

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