style(board): round overlay on all sides and hide on mobile

Apply full border-radius to hover overlay panel instead of bottom-only,
and add media query to hide the overlay on screens <= 768px since hover
is not available on touch devices.

apps/nextjs/src/components/board/items/widget-hover-overlay.module.css

@@ -34,7 +34,7 @@
   min-height: 28px;
   padding: 4px 8px;
   border: 1px solid var(--border-color);
-  border-radius: 0 0 var(--mantine-radius-md) var(--mantine-radius-md);
+  border-radius: var(--mantine-radius-md);
   background-color: var(--background-color);
   box-shadow: 0 4px 16px rgb(0 0 0 / 0.12);
   backdrop-filter: blur(8px);
@@ -108,3 +108,9 @@
   overflow: hidden;
   text-overflow: ellipsis;
 }
+
+@media (max-width: 768px) {
+  .wrapper {
+    display: none;
+  }
+}