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/common/mcp_process.rs

@@ -62,6 +62,7 @@ use codex_app_server_protocol::SkillsListParams;
 use codex_app_server_protocol::ThreadArchiveParams;
 use codex_app_server_protocol::ThreadCompactStartParams;
 use codex_app_server_protocol::ThreadForkParams;
+use codex_app_server_protocol::ThreadInjectItemsParams;
 use codex_app_server_protocol::ThreadListParams;
 use codex_app_server_protocol::ThreadLoadedListParams;
 use codex_app_server_protocol::ThreadMemoryModeSetParams;
@@ -602,6 +603,15 @@ impl McpProcess {
         self.send_request("turn/start", params).await
     }
 
+    /// Send a `thread/inject_items` JSON-RPC request (v2).
+    pub async fn send_thread_inject_items_request(
+        &mut self,
+        params: ThreadInjectItemsParams,
+    ) -> anyhow::Result<i64> {
+        let params = Some(serde_json::to_value(params)?);
+        self.send_request("thread/inject_items", params).await
+    }
+
     /// Send a `command/exec` JSON-RPC request (v2).
     pub async fn send_command_exec_request(
         &mut self,