client side modelinfo overrides (#12101)

TL;DR
Add top-level `model_catalog_json` config support so users can supply a
local model catalog override from a JSON file path (including adding new
models) without backend changes.

### Problem
Codex previously had no clean client-side way to replace/overlay model
catalog data for local testing of model metadata and new model entries.

### Fix
- Add top-level `model_catalog_json` config field (JSON file path).
- Apply catalog entries when resolving `ModelInfo`:
  1. Base resolved model metadata (remote/fallback)
  2. Catalog overlay from `model_catalog_json`
3. Existing global top-level overrides (`model_context_window`,
`model_supports_reasoning_summaries`, etc.)

### Note
Will revisit per-field overrides in a follow-up

### Tests
Added tests

codex-rs/tui/src/chatwidget/tests.rs

@@ -1580,7 +1580,7 @@ async fn make_chatwidget_manual(
     let auth_manager =
         codex_core::test_support::auth_manager_from_auth(CodexAuth::from_api_key("test"));
     let codex_home = cfg.codex_home.clone();
-    let models_manager = Arc::new(ModelsManager::new(codex_home, auth_manager.clone()));
+    let models_manager = Arc::new(ModelsManager::new(codex_home, auth_manager.clone(), None));
     let reasoning_effort = None;
     let base_mode = CollaborationMode {
         mode: ModeKind::Default,
@@ -1699,6 +1699,7 @@ fn set_chatgpt_auth(chat: &mut ChatWidget) {
     chat.models_manager = Arc::new(ModelsManager::new(
         chat.config.codex_home.clone(),
         chat.auth_manager.clone(),
+        None,
     ));
 }