[fix](trx-frontend-http): skip auto-appending rig_id when already in URL

postPath() was duplicating rig_id on /select_rig calls, causing deserialization failure and silently dropping the rig switch.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

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

@@ -3302,7 +3302,8 @@ window.trxScheduleUiFrameJob = scheduleUiFrameJob;
 
 async function postPath(path) {
   // Auto-append rig_id so each tab targets its own rig.
-  if (lastActiveRigId) {
+  // Skip when the caller already included rig_id (e.g. /select_rig).
+  if (lastActiveRigId && !path.includes("rig_id=")) {
     const sep = path.includes("?") ? "&" : "?";
     path = `${path}${sep}rig_id=${encodeURIComponent(lastActiveRigId)}`;
   }