fix: enable scroll in DirectoryPicker card area

Add min-h-0 to ScrollArea -- flex children default to min-height:auto
which prevents them from shrinking below content size. Without min-h-0,
the card grid grows to fit all content and never triggers overflow scroll.

Classic flexbox scroll fix.

Author: DevanshuNEU

frontend/src/components/DirectoryPicker.tsx

@@ -105,7 +105,7 @@ export function DirectoryPicker({
               </div>
             </div>
 
-            <ScrollArea className="flex-1 px-6">
+            <ScrollArea className="flex-1 min-h-0 px-6">
               <motion.div
                 className="flex flex-wrap gap-2 pb-4"
                 initial="hidden"