Expose plugin manifest keywords in app server (#21271)

## Summary
- Add plugin manifest keywords to core plugin marketplace/detail models
- Expose keywords on app-server v2 PluginSummary and generated
schema/types
- Populate keywords in plugin/list and plugin/read responses for local
plugins

Depends on https://github.com/openai/openai/pull/891087

## Validation
- just fmt
- just write-app-server-schema
- cargo test -p codex-app-server-protocol
- cargo test -p codex-core-plugins
- cargo test -p codex-app-server
plugin_list_keeps_valid_marketplaces_when_another_marketplace_fails_to_load
- cargo test -p codex-app-server
plugin_read_returns_plugin_details_with_bundle_contents

codex-rs/app-server-protocol/src/protocol/v2/plugin.rs

@@ -446,6 +446,8 @@ pub struct PluginSummary {
     #[serde(default)]
     pub availability: PluginAvailability,
     pub interface: Option<PluginInterface>,
+    #[serde(default)]
+    pub keywords: Vec<String>,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]

codex-rs/app-server-protocol/src/protocol/v2/tests.rs

@@ -3044,6 +3044,7 @@ fn plugin_share_list_response_serializes_share_items() {
                     auth_policy: PluginAuthPolicy::OnUse,
                     availability: PluginAvailability::Available,
                     interface: None,
+                    keywords: Vec::new(),
                 },
                 share_url: "https://chatgpt.example/plugins/share/share-key-1".to_string(),
                 local_plugin_path: None,
@@ -3062,6 +3063,7 @@ fn plugin_share_list_response_serializes_share_items() {
                     "authPolicy": "ON_USE",
                     "availability": "AVAILABLE",
                     "interface": null,
+                    "keywords": [],
                 },
                 "shareUrl": "https://chatgpt.example/plugins/share/share-key-1",
                 "localPluginPath": null,