Summary

Migrate the YHub versioning client and example to the upstream yjs/yhub API (v0.3.0+), which introduced versioned URL paths and new response shapes.

Rationale

The upstream yhub server has introduced breaking API changes (versioned URL paths, wrapped activity responses, renamed changeset fields). This PR updates the BlockNote client to match, so it works against the current upstream yhub.

Changes

• URL paths: /{endpoint}/{org}/{docId} → /{endpoint}/v1/{org}/{docId} (the baseUrl option now includes the API prefix, e.g. https://yhub.example.com/api)
• Activity response: unwrap from { activity: [...] } wrapper (3 call sites)
• Changeset response: prevDoc/nextDoc replaced with ydoc
• PATCH userid: moved from ignored ?userid= query param to by field in request body
• Rollback: removed redundant ?from= query param (body-only)
• WebSocket path: updated to /api/ws/v1 in the example
• Tests: all 29 yhub tests updated to match new response shapes and URL paths

Impact

Breaking change for baseUrl — callers must now include the API prefix (e.g. /api) in their baseUrl. The versioning example is updated accordingly.

Testing

• All 29 unit tests in yhub.test.ts pass
• End-to-end tested against a local yhub-standalone Docker container: PATCH, activity, changeset, rollback, and mergeUsers all verified working with the new API shapes

Checklist

• Code follows the project's coding standards.
• Unit tests covering the new feature have been added.
• All existing tests pass.
• The documentation has been updated to reflect the new feature