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/tui/src/chatwidget/plugins.rs

@@ -1728,6 +1728,12 @@ impl ChatWidget {
             is_disabled: true,
             ..Default::default()
         });
+        items.push(SelectionItem {
+            name: "Hooks".to_string(),
+            description: Some(plugin_hook_summary(plugin)),
+            is_disabled: true,
+            ..Default::default()
+        });
         items.push(SelectionItem {
             name: "Apps".to_string(),
             description: Some(plugin_app_summary(plugin)),
@@ -2142,6 +2148,29 @@ fn plugin_app_summary(plugin: &PluginDetail) -> String {
     }
 }
 
+fn plugin_hook_summary(plugin: &PluginDetail) -> String {
+    if plugin.hooks.is_empty() {
+        "No plugin hooks.".to_string()
+    } else {
+        let mut event_counts = Vec::<(codex_app_server_protocol::HookEventName, usize)>::new();
+        for hook in &plugin.hooks {
+            if let Some((_, handler_count)) = event_counts
+                .iter_mut()
+                .find(|(event_name, _)| *event_name == hook.event_name)
+            {
+                *handler_count += 1;
+            } else {
+                event_counts.push((hook.event_name, 1));
+            }
+        }
+        event_counts
+            .into_iter()
+            .map(|(event_name, handler_count)| format!("{event_name:?} ({handler_count})"))
+            .collect::<Vec<_>>()
+            .join(", ")
+    }
+}
+
 fn plugin_mcp_summary(plugin: &PluginDetail) -> String {
     if plugin.mcp_servers.is_empty() {
         "No plugin MCP servers.".to_string()