Split playground into workspace packages

[jderochervlk]

Context

This is stacked on top of vlk/monorepo-foundation and prepares the docs/playground split needed for guide.rescript-lang.org.

Summary

• Add packages/shared for reusable editor/compiler helpers such as CodeMirror, HighlightJs, Semver, icons, text components, and compiler API bindings.
• Add packages/playground for the current playground implementation and its direct runtime/editor dependencies.
• Wire apps/docs to depend on @rescript-lang/shared and @rescript-lang/playground through the workspace graph.
• Keep playground browser storage reads safe during prerendering so /try does not access window at build time.
• Align the Cloudflare deploy workflows with the installed Wrangler version so the deploy action does not run npm inside a workspace package with workspace:* dependencies.

Verification

• yarn build:res
• yarn build:scripts
• yarn build:update-index
• yarn build:vite
• yarn ci:format
• yarn vitest --browser.headless --run
• yarn test outside the sandbox
• GitHub PR checks: Format, Site_Checks, Vitest, Deploy, E2E Tests

[github-actions]

Cloudflare deployment

Deployement ID: 96e51657-991d-4c3c-b130-4aa8308d8a70
Deployment Environment: preview

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