Collaboration API: Write Operations

[btoron]

Overview

Implement the Collaboration API write (POST) methods in the async client.

Endpoints (4)

ID	Method	Path
CB002P	POST	chats
CB003P	POST	chats/{chatId}/leave
CB004P	POST	chats/{chatId}/messages
CB006P	POST	chats/{chatId}/participants/invite

Method count: 4 write operations (POST)

Implementation Notes

• Add POST methods to ofsc/async_client/collaboration.py (AsyncOFSCollaboration)
• Note: The Collaboration module itself is created in the corresponding GET issue
• Create corresponding request/response Pydantic models as needed
• Add tests in tests/async/test_async_collaboration.py
• Run uv run python scripts/update_endpoints_doc.py --force after implementation
• Update README with [Sync & Async] or [Async] tags

Acceptance Criteria

• All 4 POST methods implemented in AsyncOFSCollaboration
• Request/response Pydantic models created
• Mocked tests passing
• Live tests marked with @pytest.mark.uses_real_data
• ENDPOINTS.md updated