Update models.json (#18586)

- Replace the active models-manager catalog with the deleted core
catalog contents.
- Replace stale hardcoded test model slugs with current bundled model
slugs.
- Keep this as a stacked change on top of the cleanup PR.

codex-rs/core/tests/suite/override_updates.rs

@@ -26,7 +26,7 @@ fn collab_mode_with_instructions(instructions: Option<&str>) -> CollaborationMod
     CollaborationMode {
         mode: ModeKind::Default,
         settings: Settings {
-            model: "gpt-5.1".to_string(),
+            model: "gpt-5.4".to_string(),
             reasoning_effort: None,
             developer_instructions: instructions.map(str::to_string),
         },