fix: clip QuickAddAgentPopover items to container border-radius

Add overflow-hidden to PopoverContent so hover backgrounds on the
bottom item stay clipped within the rounded corners. Also restore
role=menu on the keyboard-navigable container (lost during revert).

desktop/src/features/channels/ui/QuickAddAgentPopover.tsx

@@ -301,9 +301,14 @@ export function QuickAddAgentPopover({
   return (
     <Popover open={open} onOpenChange={onOpenChange}>
       <PopoverTrigger asChild>{children}</PopoverTrigger>
-      <PopoverContent align="end" className="w-72 p-0" sideOffset={6}>
+      <PopoverContent
+        align="end"
+        className="w-72 overflow-hidden p-0"
+        sideOffset={6}
+      >
         <div
           className="flex max-h-80 flex-col"
+          role="menu"
           onKeyDown={(e) => {
             const container = e.currentTarget;
             const buttons = Array.from(
@@ -344,7 +349,11 @@ export function QuickAddAgentPopover({
                 No agents available.
               </div>
             ) : (
-              <div aria-label="Available agents" className="py-1" role="listbox">
+              <div
+                aria-label="Available agents"
+                className="py-1"
+                role="listbox"
+              >
                 {items.map((item) => {
                   const itemKey = getItemKey(item);
                   const isInChannel = item.kind === "running-in-channel";