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/codex_app_server_protocol.v2.schemas.json

@@ -1160,6 +1160,31 @@
           "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": {
@@ -10710,6 +10735,30 @@
     "ThreadId": {
       "type": "string"
     },
+    "ThreadInjectItemsParams": {
+      "$schema": "http://json-schema.org/draft-07/schema#",
+      "properties": {
+        "items": {
+          "description": "Raw Responses API items to append to the thread's model-visible history.",
+          "items": true,
+          "type": "array"
+        },
+        "threadId": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "items",
+        "threadId"
+      ],
+      "title": "ThreadInjectItemsParams",
+      "type": "object"
+    },
+    "ThreadInjectItemsResponse": {
+      "$schema": "http://json-schema.org/draft-07/schema#",
+      "title": "ThreadInjectItemsResponse",
+      "type": "object"
+    },
     "ThreadItem": {
       "oneOf": [
         {