Show plugin hooks in plugin details (#21447)

Supersedes the abandoned #19859, rebuilt on latest `main`.

# Why

PR #19705 adds discovery for hooks bundled with plugins, but `/plugins`
still only shows skills, apps, and MCP servers. This follow-up makes
bundled hooks visible in the same plugin detail view so users can
inspect the full plugin surface in one place.

We also need `PluginHookSummary` to populate Plugin Hooks in the app;
`hooks/list` is not enough there because plugin detail needs to show
hooks for disabled plugins too.

# What

- extend `plugin/read` with `PluginHookSummary` entries for bundled
hooks
- summarize plugin hooks while loading plugin details
- render a `Hooks` row in the `/plugins` detail popup

<img width="3456" height="848" alt="CleanShot 2026-04-27 at 11 45 34@2x"
src="https://github.com/user-attachments/assets/fe3a38d6-a260-4351-8513-fb04c93d725b"
/>

codex-rs/app-server/src/request_processors/plugins.rs

@@ -615,6 +615,15 @@ impl PluginRequestProcessor {
                         &visible_skills,
                         &outcome.plugin.disabled_skill_paths,
                     ),
+                    hooks: outcome
+                        .plugin
+                        .hooks
+                        .into_iter()
+                        .map(|hook| codex_app_server_protocol::PluginHookSummary {
+                            key: hook.key,
+                            event_name: hook.event_name.into(),
+                        })
+                        .collect(),
                     apps: app_summaries,
                     mcp_servers: outcome.plugin.mcp_server_names,
                 }
@@ -1490,6 +1499,7 @@ fn remote_plugin_detail_to_info(
                 enabled: skill.enabled,
             })
             .collect(),
+        hooks: Vec::new(),
         apps,
         mcp_servers: Vec::new(),
     }