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/core/src/thread_manager.rs

@@ -21,6 +21,7 @@ use crate::skills::SkillsManager;
 use codex_protocol::ThreadId;
 use codex_protocol::config_types::CollaborationModeMask;
 use codex_protocol::openai_models::ModelPreset;
+use codex_protocol::openai_models::ModelsResponse;
 use codex_protocol::protocol::InitialHistory;
 use codex_protocol::protocol::McpServerRefreshConfig;
 use codex_protocol::protocol::Op;
@@ -141,6 +142,7 @@ impl ThreadManager {
         codex_home: PathBuf,
         auth_manager: Arc<AuthManager>,
         session_source: SessionSource,
+        model_catalog: Option<ModelsResponse>,
     ) -> Self {
         let (thread_created_tx, _) = broadcast::channel(THREAD_CREATED_CHANNEL_CAPACITY);
         let skills_manager = Arc::new(SkillsManager::new(codex_home.clone()));
@@ -149,7 +151,11 @@ impl ThreadManager {
             state: Arc::new(ThreadManagerState {
                 threads: Arc::new(RwLock::new(HashMap::new())),
                 thread_created_tx,
-                models_manager: Arc::new(ModelsManager::new(codex_home, auth_manager.clone())),
+                models_manager: Arc::new(ModelsManager::new(
+                    codex_home,
+                    auth_manager.clone(),
+                    model_catalog,
+                )),
                 skills_manager,
                 file_watcher,
                 auth_manager,