fix(ui): prevent modal overlays from inheriting margin-top from parent space-y containers

frontend/src/components/MobileHeaderMenu.tsx

@@ -13,10 +13,10 @@ export const MobileHeaderMenu: React.FC<MobileHeaderMenuProps> = ({ activeTabLab
   if (!isMenuOpen) return null;
 
   return (
-    <div className="sm:hidden fixed inset-0 z-50">
+    <div className="sm:hidden fixed inset-0 !m-0 z-50">
       {/* Backdrop */}
       <div
-        className="fixed inset-0 bg-black/60 backdrop-blur-xs animate-in fade-in duration-150"
+        className="fixed inset-0 !m-0 bg-black/60 backdrop-blur-xs animate-in fade-in duration-150"
         onClick={() => {
           triggerHaptic(8);
           closeMenu();

frontend/src/components/UnifiedShareModal.tsx

@@ -96,7 +96,7 @@ export const UnifiedShareModal: React.FC<UnifiedShareModalProps> = ({
 
   return (
     <div
-      className="fixed inset-0 z-50 flex items-center justify-center p-4 bg-black/60 backdrop-blur-xs"
+      className="fixed inset-0 !m-0 modal-overlay z-50 flex items-center justify-center p-4 bg-black/60 backdrop-blur-xs"
       onClick={(e) => {
         if (e.target === e.currentTarget) onClose();
       }}