Support model catalog Apps usage instructions (#61213)

## What changed

- Add the disabled-by-default `catalog_apps_instructions` feature to use the selected model's `model_messages.apps.usage_instructions`, subject to existing Apps availability and model gates.
- Preserve valid catalog text literally, allow an empty string to clear guidance, and fall back to bundled instructions for missing, whitespace-only, or oversized values. Overrides are limited to 800 UTF-8 bytes.
- Reconcile guidance with the latest retained Apps fragment, emitting replacement or removal notices when needed and avoiding repeated updates across resumes. Preserve compatibility with bundled guidance and legacy checkpoints.
- Recognize catalog Apps fragments as contextual developer messages in event mapping and rollout rollback.

## Testing

Add resolver, world-state, client, and scenario coverage for literal text and byte limits, feature and availability gates, model switches, clearing guidance, resumes, and legacy history recovery.

GitOrigin-RevId: 6240d407ada8f22fa101753ff3ddb338632ae283

codex-rs/core/src/apps/render.rs

@@ -9,7 +9,7 @@ pub(crate) fn render_apps_section(connectors: &[AppInfo]) -> Option<String> {
     connectors
         .iter()
         .any(|connector| connector.is_accessible && connector.is_enabled)
-        .then(|| AppsInstructions.render().expect_text())
+        .then(|| AppsInstructions::default().render().expect_text())
 }
 
 #[cfg(test)]