feat: UI improvements — scrollbar, multi-filters, pricing fix, routing, modals

- Global page scrollbar styled with gold theme
- Schedule: multi-select for class types and status tags
- Pricing: fix tab switch blink (display toggle vs conditional render)
- OpenDay: trainer name more prominent, section divider added
- Team: browser back button closes trainer bio (history API)
- Modals: block scroll + compensate scrollbar width to prevent layout shift
- Header: remove booking button from desktop nav

src/components/ui/SignupModal.tsx

@@ -74,9 +74,15 @@ export function SignupModal({
   }, [open, onClose]);
 
   useEffect(() => {
-    if (open) document.body.style.overflow = "hidden";
-    else document.body.style.overflow = "";
-    return () => { document.body.style.overflow = ""; };
+    if (open) {
+      const scrollbarWidth = window.innerWidth - document.documentElement.clientWidth;
+      document.body.style.overflow = "hidden";
+      document.body.style.paddingRight = `${scrollbarWidth}px`;
+    } else {
+      document.body.style.overflow = "";
+      document.body.style.paddingRight = "";
+    }
+    return () => { document.body.style.overflow = ""; document.body.style.paddingRight = ""; };
   }, [open]);
 
   const handleSubmit = useCallback(async (e: React.FormEvent) => {