log plugin MCP server names (#26002)

## Summary
- emit the plugin capability summary's exact MCP server names in
`codex_plugin_used`

## Test
- `just test -p codex-analytics`
- `just test -p codex-core
explicit_plugin_mentions_track_plugin_used_analytics`
- `just fix -p codex-analytics`

codex-rs/analytics/src/events.rs

@@ -865,6 +865,7 @@ pub(crate) struct CodexPluginMetadata {
 pub(crate) struct CodexPluginUsedMetadata {
     #[serde(flatten)]
     pub(crate) plugin: CodexPluginMetadata,
+    pub(crate) mcp_server_names: Option<Vec<String>>,
     pub(crate) thread_id: Option<String>,
     pub(crate) turn_id: Option<String>,
     pub(crate) model_slug: Option<String>,
@@ -971,8 +972,13 @@ pub(crate) fn codex_plugin_used_metadata(
     tracking: &TrackEventsContext,
     plugin: PluginTelemetryMetadata,
 ) -> CodexPluginUsedMetadata {
+    let mcp_server_names = plugin
+        .capability_summary
+        .as_ref()
+        .map(|summary| summary.mcp_server_names.clone());
     CodexPluginUsedMetadata {
         plugin: codex_plugin_metadata(plugin),
+        mcp_server_names,
         thread_id: Some(tracking.thread_id.clone()),
         turn_id: Some(tracking.turn_id.clone()),
         model_slug: Some(tracking.model_slug.clone()),