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/app-server-protocol/src/protocol/common.rs

@@ -581,6 +581,11 @@ client_request_definitions! {
         serialization: global("config"),
         response: v2::SkillsListResponse,
     },
+    HooksList => "hooks/list" {
+        params: v2::HooksListParams,
+        serialization: global("config"),
+        response: v2::HooksListResponse,
+    },
     MarketplaceAdd => "marketplace/add" {
         params: v2::MarketplaceAddParams,
         serialization: global("config"),