[feat](trx-client): support rig display names in frontend layer

Add display_name field to RemoteRigEntry and propagate from GetRigs
response. Update http-json frontend to include display_name in rig
entries.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/trx-client/trx-frontend/trx-frontend-http-json/src/server.rs

@@ -243,6 +243,7 @@ fn snapshot_remote_rigs(context: &FrontendRuntimeContext) -> Vec<RigEntry> {
                 .iter()
                 .map(|entry| RigEntry {
                     rig_id: entry.rig_id.clone(),
+                    display_name: entry.display_name.clone(),
                     state: entry.state.clone(),
                     audio_port: entry.audio_port,
                 })