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/core-plugins/src/manager_tests.rs

@@ -25,6 +25,7 @@ use codex_config::McpServerConfig;
 use codex_config::McpServerToolConfig;
 use codex_config::types::McpServerTransportConfig;
 use codex_login::CodexAuth;
+use codex_protocol::protocol::HookEventName;
 use codex_protocol::protocol::Product;
 use codex_utils_absolute_path::test_support::PathBufExt;
 use pretty_assertions::assert_eq;
@@ -1933,13 +1934,48 @@ async fn read_plugin_for_config_installed_git_source_reads_from_cache_without_cl
         &cached_plugin_root.join(".mcp.json"),
         r#"{"mcpServers":{"toolkit":{"command":"toolkit-mcp"}}}"#,
     );
+    write_file(
+        &cached_plugin_root.join("hooks/hooks.json"),
+        r#"{
+  "hooks": {
+    "SessionStart": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "echo startup"
+          }
+        ]
+      }
+    ],
+    "PreToolUse": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "echo first"
+          },
+          {
+            "type": "command",
+            "command": "echo second"
+          }
+        ]
+      }
+    ]
+  }
+}"#,
+    );
     write_file(
         &tmp.path().join(CONFIG_TOML_FILE),
         r#"[features]
 plugins = true
+plugin_hooks = true
 
 [plugins."toolkit@debug"]
 enabled = true
+
+[hooks.state."toolkit@debug:hooks/hooks.json:pre_tool_use:0:0"]
+enabled = false
 "#,
     );
 
@@ -1978,6 +2014,23 @@ enabled = true
         outcome.plugin.apps,
         vec![AppConnectorId("connector_calendar".to_string())]
     );
+    assert_eq!(
+        outcome.plugin.hooks,
+        vec![
+            PluginHookSummary {
+                key: "toolkit@debug:hooks/hooks.json:pre_tool_use:0:0".to_string(),
+                event_name: HookEventName::PreToolUse,
+            },
+            PluginHookSummary {
+                key: "toolkit@debug:hooks/hooks.json:pre_tool_use:0:1".to_string(),
+                event_name: HookEventName::PreToolUse,
+            },
+            PluginHookSummary {
+                key: "toolkit@debug:hooks/hooks.json:session_start:0:0".to_string(),
+                event_name: HookEventName::SessionStart,
+            },
+        ]
+    );
     assert_eq!(outcome.plugin.mcp_server_names, vec!["toolkit".to_string()]);
     assert!(
         !tmp.path()