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/schema/json/codex_app_server_protocol.v2.schemas.json

@@ -1348,6 +1348,30 @@
           "title": "Skills/listRequest",
           "type": "object"
         },
+        {
+          "properties": {
+            "id": {
+              "$ref": "#/definitions/RequestId"
+            },
+            "method": {
+              "enum": [
+                "hooks/list"
+              ],
+              "title": "Hooks/listRequestMethod",
+              "type": "string"
+            },
+            "params": {
+              "$ref": "#/definitions/HooksListParams"
+            }
+          },
+          "required": [
+            "id",
+            "method",
+            "params"
+          ],
+          "title": "Hooks/listRequest",
+          "type": "object"
+        },
         {
           "properties": {
             "id": {
@@ -6178,6 +6202,21 @@
       "title": "HookCompletedNotification",
       "type": "object"
     },
+    "HookErrorInfo": {
+      "properties": {
+        "message": {
+          "type": "string"
+        },
+        "path": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "message",
+        "path"
+      ],
+      "type": "object"
+    },
     "HookEventName": {
       "enum": [
         "preToolUse",
@@ -6204,6 +6243,64 @@
       ],
       "type": "string"
     },
+    "HookMetadata": {
+      "properties": {
+        "command": {
+          "type": [
+            "string",
+            "null"
+          ]
+        },
+        "displayOrder": {
+          "format": "int64",
+          "type": "integer"
+        },
+        "eventName": {
+          "$ref": "#/definitions/HookEventName"
+        },
+        "handlerType": {
+          "$ref": "#/definitions/HookHandlerType"
+        },
+        "matcher": {
+          "type": [
+            "string",
+            "null"
+          ]
+        },
+        "pluginId": {
+          "type": [
+            "string",
+            "null"
+          ]
+        },
+        "source": {
+          "$ref": "#/definitions/HookSource"
+        },
+        "sourcePath": {
+          "$ref": "#/definitions/AbsolutePathBuf"
+        },
+        "statusMessage": {
+          "type": [
+            "string",
+            "null"
+          ]
+        },
+        "timeoutSec": {
+          "format": "uint64",
+          "minimum": 0.0,
+          "type": "integer"
+        }
+      },
+      "required": [
+        "displayOrder",
+        "eventName",
+        "handlerType",
+        "source",
+        "sourcePath",
+        "timeoutSec"
+      ],
+      "type": "object"
+    },
     "HookMigration": {
       "properties": {
         "name": {
@@ -6389,6 +6486,68 @@
       "title": "HookStartedNotification",
       "type": "object"
     },
+    "HooksListEntry": {
+      "properties": {
+        "cwd": {
+          "type": "string"
+        },
+        "errors": {
+          "items": {
+            "$ref": "#/definitions/HookErrorInfo"
+          },
+          "type": "array"
+        },
+        "hooks": {
+          "items": {
+            "$ref": "#/definitions/HookMetadata"
+          },
+          "type": "array"
+        },
+        "warnings": {
+          "items": {
+            "type": "string"
+          },
+          "type": "array"
+        }
+      },
+      "required": [
+        "cwd",
+        "errors",
+        "hooks",
+        "warnings"
+      ],
+      "type": "object"
+    },
+    "HooksListParams": {
+      "$schema": "http://json-schema.org/draft-07/schema#",
+      "properties": {
+        "cwds": {
+          "description": "When empty, defaults to the current session working directory.",
+          "items": {
+            "type": "string"
+          },
+          "type": "array"
+        }
+      },
+      "title": "HooksListParams",
+      "type": "object"
+    },
+    "HooksListResponse": {
+      "$schema": "http://json-schema.org/draft-07/schema#",
+      "properties": {
+        "data": {
+          "items": {
+            "$ref": "#/definitions/HooksListEntry"
+          },
+          "type": "array"
+        }
+      },
+      "required": [
+        "data"
+      ],
+      "title": "HooksListResponse",
+      "type": "object"
+    },
     "ImageDetail": {
       "enum": [
         "auto",