Add turn item injection API (#17703)

## 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)

codex-rs/app-server/tests/suite/v2/mod.rs

@@ -35,6 +35,7 @@ mod safety_check_downgrade;
 mod skills_list;
 mod thread_archive;
 mod thread_fork;
+mod thread_inject_items;
 mod thread_list;
 mod thread_loaded_list;
 mod thread_memory_mode_set;