docs: Document experimental native Go workspaces (#13963)
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### Description
Documents experimental native Go workspace support, including setup,
built-in tasks, caching, affectedness, pruning, limitations, and
rollback to package-script integration.
Updates multi-language guidance and contributor architecture
documentation to reflect native Go behavior.
Closes TURBO-5966
### Testing Instructions
```bash
pnpm --filter docs check-links
OG_IMAGE_SECRET="0000000000000000000000000000000000000000000000000000000000000000" turbo run build --filter=docs
```
<!-- CURSOR_AGENT_PR_BODY_END -->
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Co-authored-by: Cursor Agent <cursoragent@cursor.com>