Drop overlay sits above the artifact sheet below lg

Beside the panel (lg and up) it still covers only the chat column. Below
lg the panel is a fixed z-40 sheet, so the overlay covers the window at
z-[45] (under the z-50 mobile drawer) instead of being hidden by it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

raggr-frontend/src/components/DropOverlay.tsx

@@ -10,7 +10,9 @@ type DropOverlayProps = {
 
 /**
  * Listens for file drags anywhere in the window and covers its positioned
- * parent with a "Drop to attach" target. Drags without files (text, links)
+ * parent (the chat column, beside the artifact panel) with a "Drop to attach"
+ * target. Below lg the panel is a full-screen sheet, so it covers the window
+ * and sits above the sheet. Drags without files (text, links)
  * are ignored so they keep their normal behaviour.
  */
 export const DropOverlay = ({ onDrop }: DropOverlayProps) => {
@@ -65,7 +67,7 @@ export const DropOverlay = ({ onDrop }: DropOverlayProps) => {
 
   return (
     <div
-      className="pointer-events-none absolute inset-0 z-[45] flex items-center justify-center bg-cream/80 backdrop-blur-sm p-3 md:p-5"
+      className="pointer-events-none fixed lg:absolute inset-0 z-[45] flex items-center justify-center bg-cream/80 backdrop-blur-sm p-3 md:p-5"
       data-testid="drop-overlay"
     >
       <div className="w-full h-full rounded-3xl border-2 border-dashed border-amber-glow/50 bg-amber-pale/70 flex flex-col items-center justify-center gap-3 message-enter">