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/tests/common/mcp_process.rs

@@ -37,6 +37,7 @@ use codex_app_server_protocol::FsWriteFileParams;
 use codex_app_server_protocol::GetAccountParams;
 use codex_app_server_protocol::GetAuthStatusParams;
 use codex_app_server_protocol::GetConversationSummaryParams;
+use codex_app_server_protocol::HooksListParams;
 use codex_app_server_protocol::InitializeCapabilities;
 use codex_app_server_protocol::InitializeParams;
 use codex_app_server_protocol::JSONRPCError;
@@ -580,6 +581,15 @@ impl McpProcess {
         self.send_request("skills/list", params).await
     }
 
+    /// Send a `hooks/list` JSON-RPC request.
+    pub async fn send_hooks_list_request(
+        &mut self,
+        params: HooksListParams,
+    ) -> anyhow::Result<i64> {
+        let params = Some(serde_json::to_value(params)?);
+        self.send_request("hooks/list", params).await
+    }
+
     /// Send a `marketplace/add` JSON-RPC request.
     pub async fn send_marketplace_add_request(
         &mut self,