[codex] Forward turn moderation metadata through app-server (#25710)

## Why
First-party backends can supply turn-scoped moderation metadata that
app-server clients need for client-side presentation. Exposing this as
an experimental typed notification lets opted-in clients consume it
without interpreting raw Responses API events.

## What changed
- forward `response.metadata.openai_chatgpt_moderation_metadata` from
Responses API SSE and WebSocket streams as turn-scoped moderation
metadata
- emit the experimental app-server v2 `turn/moderationMetadata`
notification with `{ threadId, turnId, metadata }`
- add app-server integration coverage for the typed moderation metadata
notification

## Testing
- `just test -p codex-core
build_ws_client_metadata_includes_window_lineage_and_turn_metadata`
- `just test -p codex-core` (fails locally: 46 failures and 1 timeout,
primarily missing `test_stdio_server` and shell snapshot timeouts)
- `just test -p codex-app-server-protocol`
- `just test -p codex-app-server
turn_moderation_metadata_emits_typed_notification_v2`
- `just test -p codex-app-server` (fails locally: 792 passed, 10 failed,
and 5 timed out; failures are in existing environment-sensitive tests,
primarily because nested macOS `sandbox-exec` is not permitted)
- `just write-app-server-schema --experimental --schema-root
/tmp/codex-app-server-schema-experimental`

codex-rs/app-server-protocol/src/protocol/v2/model.rs

@@ -8,6 +8,7 @@ use codex_protocol::protocol::ModelVerification as CoreModelVerification;
 use schemars::JsonSchema;
 use serde::Deserialize;
 use serde::Serialize;
+use serde_json::Value as JsonValue;
 use ts_rs::TS;
 
 v2_enum_from_core!(
@@ -152,3 +153,12 @@ pub struct ModelVerificationNotification {
     pub turn_id: String,
     pub verifications: Vec<ModelVerification>,
 }
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct TurnModerationMetadataNotification {
+    pub thread_id: String,
+    pub turn_id: String,
+    pub metadata: JsonValue,
+}