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)]