Support catalog templates for approved command prefixes (#55366)

## What changed

Add `approved_prefixes` to catalog permission messages, with `{{ approved_prefixes }}` substitution for the approved command list. An empty template suppresses the section; missing or null values retain the bundled template.

For `on-request` approvals, append an explicitly supplied prefix template even when the catalog also supplies approval instructions. Use the template for bundled `on-request` and granular approval instructions as well.

## Testing

Extend the remote model catalog integration test to cover custom prefix rendering alongside catalog approval instructions and suppression with an empty template.

GitOrigin-RevId: 82dd6f83caa56cab0a2f6343bf912efe2cb97d64

codex-rs/core/src/context/world_state/permissions_tests.rs

@@ -268,6 +268,7 @@ fn permissions_state(
         danger_full_access: Some("Full access.".to_string()),
         workspace_write: Some("Workspace write.".to_string()),
         read_only: Some("Read only.".to_string()),
+        approved_prefixes: None,
     };
     let mut model = model_info_from_slug("test-model");
     model.model_messages = Some(ModelMessages {