Add turn item injection API

[pakrym-oai]

Summary

• Add turn/inject_items app-server v2 request support for appending raw Responses API items to a loaded thread history without starting a turn.
• Generate JSON schema and TypeScript protocol artifacts for the new params and empty response.
• Document the new endpoint and include a request/response example.
• Preserve compatibility with the typo alias turn/injet_items while returning the canonical method name.

Testing

• Not run (not requested)

[andmis]

TY!