[fix](trx-frontend-http): scope channel audio by remote

Send the selected remote together with virtual-channel audio requests and use per-rig stream info when /audio is opened with channel_id.

This keeps browser channel audio aligned with the requested remote after the recent multi-rig client changes.

Add coverage for parsing channel_id together with remote.

Co-authored-by: OpenAI Codex <noreply@openai.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js

@@ -7672,7 +7672,10 @@ function startRxAudio() {
   const proto = location.protocol === "https:" ? "wss:" : "ws:";
   let audioPath;
   if (_audioChannelOverride) {
-    audioPath = `/audio?channel_id=${encodeURIComponent(_audioChannelOverride)}`;
+    const remoteParam = lastActiveRigId
+      ? `&remote=${encodeURIComponent(lastActiveRigId)}`
+      : "";
+    audioPath = `/audio?channel_id=${encodeURIComponent(_audioChannelOverride)}${remoteParam}`;
   } else if (lastActiveRigId) {
     audioPath = `/audio?remote=${encodeURIComponent(lastActiveRigId)}`;
   } else {