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-protocol/src/protocol/common.rs

@@ -322,6 +322,11 @@ client_request_definitions! {
         params: v2::ThreadReadParams,
         response: v2::ThreadReadResponse,
     },
+    /// Append raw Responses API items to the thread history without starting a user turn.
+    ThreadInjectItems => "thread/inject_items" {
+        params: v2::ThreadInjectItemsParams,
+        response: v2::ThreadInjectItemsResponse,
+    },
     SkillsList => "skills/list" {
         params: v2::SkillsListParams,
         response: v2::SkillsListResponse,