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/v2.rs

@@ -4251,6 +4251,20 @@ pub struct TurnStartResponse {
     pub turn: Turn,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct ThreadInjectItemsParams {
+    pub thread_id: String,
+    /// Raw Responses API items to append to the thread's model-visible history.
+    pub items: Vec<JsonValue>,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct ThreadInjectItemsResponse {}
+
 #[derive(
     Serialize, Deserialize, Debug, Default, Clone, PartialEq, JsonSchema, TS, ExperimentalApi,
 )]