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/schema/json/ClientRequest.json

@@ -2715,6 +2715,23 @@
       ],
       "type": "object"
     },
+    "ThreadInjectItemsParams": {
+      "properties": {
+        "items": {
+          "description": "Raw Responses API items to append to the thread's model-visible history.",
+          "items": true,
+          "type": "array"
+        },
+        "threadId": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "items",
+        "threadId"
+      ],
+      "type": "object"
+    },
     "ThreadListParams": {
       "properties": {
         "archived": {
@@ -3959,6 +3976,31 @@
       "title": "Thread/readRequest",
       "type": "object"
     },
+    {
+      "description": "Append raw Responses API items to the thread history without starting a user turn.",
+      "properties": {
+        "id": {
+          "$ref": "#/definitions/RequestId"
+        },
+        "method": {
+          "enum": [
+            "thread/inject_items"
+          ],
+          "title": "Thread/injectItemsRequestMethod",
+          "type": "string"
+        },
+        "params": {
+          "$ref": "#/definitions/ThreadInjectItemsParams"
+        }
+      },
+      "required": [
+        "id",
+        "method",
+        "params"
+      ],
+      "title": "Thread/injectItemsRequest",
+      "type": "object"
+    },
     {
       "properties": {
         "id": {