[codex] Add user input client ids (#24653)

## Summary

Adds an optional `clientId` field to app-server v2 `UserInput` and
carries it through the core `UserInput` model so clients can correlate
echoed user input items without relying on payload equality.

## Details

- Adds `client_id: Option<String>` to core `UserInput` variants.
- Exposes the v2 app-server field as `clientId` on the wire and in
generated TypeScript.
- Preserves the id when converting between app-server v2 and core
protocol types.
- Regenerates app-server schema fixtures.

## Validation

- `just fmt`
- `just write-app-server-schema`
- `cargo test -p codex-app-server-protocol`
- `cargo test -p codex-protocol`
- `just fix -p codex-app-server-protocol`
- `just fix -p codex-protocol`
- `git diff --check`

codex-rs/app-server-protocol/schema/json/ClientRequest.json

@@ -3985,6 +3985,12 @@
           ],
           "description": "Override where approval requests are routed for review on this turn and subsequent turns."
         },
+        "clientUserMessageId": {
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "cwd": {
           "description": "Override the working directory for this turn and subsequent turns.",
           "type": [
@@ -4071,6 +4077,12 @@
     },
     "TurnSteerParams": {
       "properties": {
+        "clientUserMessageId": {
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "expectedTurnId": {
           "description": "Required active turn id precondition. The request fails when it does not match the currently active turn.",
           "type": "string"