feat: add light/dark theme to exchange instances with hub SSO sync

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

manual_trading_hub/static/app.js

@@ -56,6 +56,9 @@
     const next = nextPath || "/";
     const q = new URLSearchParams({ exchange_id: String(exchangeId), next });
     if (options.embed) q.set("embed", "1");
+    if (globalThis.HubTheme && typeof HubTheme.get === "function") {
+      q.set("hub_theme", HubTheme.get());
+    }
     const r = await apiFetch("/api/instance/open-url?" + q.toString());
     const j = await r.json();
     if (!j.ok || !j.url) {
@@ -135,6 +138,16 @@
     shell.classList.remove("hidden");
     shell.setAttribute("aria-hidden", "false");
     document.body.classList.add("hub-instance-frame-open");
+    frame.addEventListener("load", function syncInstanceFrameTheme() {
+      try {
+        if (globalThis.HubTheme && typeof HubTheme.get === "function" && frame.contentWindow) {
+          frame.contentWindow.postMessage(
+            { type: "hub-theme-sync", theme: HubTheme.get() },
+            "*"
+          );
+        }
+      } catch (_) {}
+    });
   }
 
   function closeInstanceFrame() {