Emit analytics for remote plugin installs (#20267)

## Summary

- emit `codex_plugin_installed` after a remote plugin install succeeds
- keep local installs unchanged, but let remote installs override the
analytics `plugin_id` with the backend remote plugin id
(`plugins~Plugin_...`)
- preserve the local/display identity in `plugin_name` and
`marketplace_name`, plus capability metadata from the installed bundle
- add regression coverage for local install analytics, remote install
analytics, and analytics id override serialization

## Testing

- `just fmt`
- `cargo test -p codex-analytics`
- `cargo test -p codex-app-server`

codex-rs/core-plugins/src/loader.rs

@@ -927,6 +927,7 @@ pub async fn plugin_telemetry_metadata_from_root(
 
     PluginTelemetryMetadata {
         plugin_id: plugin_id.clone(),
+        remote_plugin_id: None,
         capability_summary: Some(PluginCapabilitySummary {
             config_name: plugin_id.as_key(),
             display_name: plugin_id.plugin_name.clone(),