Avoid hub iframe overlay on embed shell tab switches.

Use in-shell content loading state instead of parent postMessage so tab changes do not trigger the full instance-frame loading mask.

Co-authored-by: Cursor <cursoragent@cursor.com>

manual_trading_hub/static/app.js

@@ -3368,6 +3368,7 @@
         const d = ev.data;
         if (!d || typeof d !== "object") return;
         if (d.type === "instance-frame-navigating") {
+          if (d.embedShellTab) return;
           setInstanceFrameNavLoading(true);
         } else if (d.type === "instance-frame-ready") {
           setInstanceFrameNavLoading(false);