Honor layered configuration when loading plugins (#40954)

## What changed

- Resolve plugin activation, MCP server policy, and marketplace definitions from the effective configuration stack, including system settings and trusted project overrides.
- Load plugin skills independently for each working directory passed to `skills/list`.
- Exclude project configuration from catalog requests whose `cwds` are omitted or empty.
- Cache up to eight loaded plugin configurations with least-recently-used eviction so requests for different working directories can reuse their results.

## Testing

- Cover layered plugin and MCP policy across trusted and untrusted projects.
- Cover per-directory skill and plugin catalog results, cache reuse and eviction, and system-defined marketplaces.

GitOrigin-RevId: cb68b2b1bdab1da48e05ca7562bc05014431fc71

codex-rs/cli/src/marketplace_cmd.rs

@@ -335,10 +335,8 @@ fn configured_marketplace_sources_by_root(
     plugins_input: &PluginsConfigInput,
 ) -> HashMap<PathBuf, JsonMarketplaceSource> {
     let marketplace_sources = configured_marketplace_sources(plugins_input, codex_home);
-    let Some(user_config) = plugins_input.config_layer_stack.effective_user_config() else {
-        return HashMap::new();
-    };
-    let Some(marketplaces) = user_config
+    let effective_config = plugins_input.config_layer_stack.effective_config();
+    let Some(marketplaces) = effective_config
         .get("marketplaces")
         .and_then(toml::Value::as_table)
     else {