Route curated plugin catalogs by authentication mode (#38429)

## Why

The model provider does not reliably identify which curated plugin catalog is
available. ChatGPT authentication can be used with a custom provider, while an
unauthenticated session should use the API-compatible catalog regardless of its
provider.

## What changed

- Select the ChatGPT curated catalog only for authentication modes that use the
  Codex backend; use the API curated catalog for API-key and unauthenticated
  sessions.
- Initialize standalone plugin managers with the current authentication mode
  across CLI, app-server, MCP, and external-agent migration paths.
- Preserve authentication mode while detecting and importing migrated plugins.

## Testing

- Cover catalog and skill routing across ChatGPT, API-key, unauthenticated,
  Bedrock, and custom-provider configurations.
- Verify authenticated plugin migration uses the ChatGPT curated marketplace.

GitOrigin-RevId: 660a339ee8891c33aad961078d3a979242a6a166

codex-rs/core/src/plugins/mod.rs

@@ -11,6 +11,7 @@ pub(crate) mod test_support;
 
 use crate::config::Config;
 use codex_core_plugins::PluginsManager;
+use codex_protocol::auth::AuthMode;
 use codex_skills_extension::HostSkillsService;
 use std::sync::Arc;
 
@@ -28,10 +29,14 @@ pub(crate) use mentions::collect_tool_mentions_from_messages;
 /// Constructs a standalone plugin manager with extension-owned plugin skill loading.
 ///
 /// Callers that already own a host skills service should inject that existing service instead.
-pub fn plugins_manager_for_config(config: &Config) -> PluginsManager {
+pub fn plugins_manager_for_config(config: &Config, auth_mode: Option<AuthMode>) -> PluginsManager {
     let skill_root_loader = Arc::new(HostSkillsService::new(
         config.codex_home.clone(),
         /*bundled_skills_enabled*/ false,
     ));
-    PluginsManager::new(config.codex_home.to_path_buf(), skill_root_loader)
+    PluginsManager::new(
+        config.codex_home.to_path_buf(),
+        auth_mode,
+        skill_root_loader,
+    )
 }