Add hooks/list app-server RPC (#19778)

## Why

We need a way to list the available hooks to expose via the TUI and App
so users can view and manage their hooks

## What

- Adds `hooks/list` for one or more `cwd` values that returns discovered
hook metadata

## Stack

1. openai/codex#19705
2. This PR - openai/codex#19778
3. openai/codex#19840
4. openai/codex#19882

## Review Notes

The generated schema files account for most of the raw diff, these files
have the core change:

- `hooks/src/engine/discovery.rs` builds the inventory entries during
hook discovery while leaving runtime handlers focused on execution.
- `app-server/src/codex_message_processor.rs` wires `hooks/list` into
the app-server flow for each requested `cwd`.
- `app-server-protocol/src/protocol/v2.rs` defines the new v2
request/response payloads exposed on the wire.

### Core Changes

`core/src/plugins/manager.rs` adds `plugins_for_layer_stack(...)` so
`skills/list` and `hooks/list`can resolve plugin state for each
requested `cwd`

---------

Co-authored-by: Codex <noreply@openai.com>

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

@@ -112,6 +112,7 @@ pub async fn load_plugins_from_layer_stack(
     extra_plugins: HashMap<String, PluginConfig>,
     store: &PluginStore,
     restriction_product: Option<Product>,
+    plugin_hooks_enabled: bool,
 ) -> PluginLoadOutcome<McpServerConfig> {
     let skill_config_rules = skill_config_rules_from_stack(config_layer_stack);
     let mut configured_plugins = configured_plugins_from_stack(config_layer_stack);
@@ -128,6 +129,7 @@ pub async fn load_plugins_from_layer_stack(
             store,
             restriction_product,
             &skill_config_rules,
+            plugin_hooks_enabled,
         )
         .await;
         for name in loaded_plugin.mcp_servers.keys() {
@@ -497,6 +499,7 @@ async fn load_plugin(
     store: &PluginStore,
     restriction_product: Option<Product>,
     skill_config_rules: &SkillConfigRules,
+    plugin_hooks_enabled: bool,
 ) -> LoadedPlugin<McpServerConfig> {
     let plugin_id = PluginId::parse(&config_name);
     let active_plugin_root = plugin_id
@@ -593,14 +596,16 @@ async fn load_plugin(
     }
     loaded_plugin.mcp_servers = mcp_servers;
     loaded_plugin.apps = load_plugin_apps(plugin_root.as_path()).await;
-    let (hook_sources, hook_load_warnings) = load_plugin_hooks(
-        &plugin_root,
-        &loaded_plugin_id,
-        &store.plugin_data_root(&loaded_plugin_id),
-        manifest_paths,
-    );
-    loaded_plugin.hook_sources = hook_sources;
-    loaded_plugin.hook_load_warnings = hook_load_warnings;
+    if plugin_hooks_enabled {
+        let (hook_sources, hook_load_warnings) = load_plugin_hooks(
+            &plugin_root,
+            &loaded_plugin_id,
+            &store.plugin_data_root(&loaded_plugin_id),
+            manifest_paths,
+        );
+        loaded_plugin.hook_sources = hook_sources;
+        loaded_plugin.hook_load_warnings = hook_load_warnings;
+    }
     loaded_plugin
 }