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/hooks/src/lib.rs

@@ -5,6 +5,7 @@ mod registry;
 mod schema;
 mod types;
 
+pub use engine::HookListEntry;
 /// Hook event names as they appear in hooks JSON and config files.
 pub const HOOK_EVENT_NAMES: [&str; 6] = [
     "PreToolUse",
@@ -26,7 +27,6 @@ pub const HOOK_EVENT_NAMES_WITH_MATCHERS: [&str; 4] = [
     "PostToolUse",
     "SessionStart",
 ];
-
 pub use events::permission_request::PermissionRequestDecision;
 pub use events::permission_request::PermissionRequestOutcome;
 pub use events::permission_request::PermissionRequestRequest;
@@ -43,9 +43,11 @@ pub use events::user_prompt_submit::UserPromptSubmitOutcome;
 pub use events::user_prompt_submit::UserPromptSubmitRequest;
 pub use legacy_notify::legacy_notify_json;
 pub use legacy_notify::notify_hook;
+pub use registry::HookListOutcome;
 pub use registry::Hooks;
 pub use registry::HooksConfig;
 pub use registry::command_from_argv;
+pub use registry::list_hooks;
 pub use schema::write_schema_fixtures;
 pub use types::Hook;
 pub use types::HookEvent;