✨(frontend) implement persistent notifications for waiting participants

Add special non-closing notifications for waiting participants that remain
visible until all have been reviewed. Implement complementary system alongside
existing toaster notifications.

Designed with accessibility in mind but would benefit from expert review.
Current UX provides good foundation with quick actions planned for v2.

src/frontend/src/components/Avatar.tsx

@@ -26,6 +26,11 @@ const avatar = cva({
         height: '100%',
       },
     },
+    notification: {
+      true: {
+        border: '2px solid white',
+      },
+    },
   },
   defaultVariants: {
     context: 'list',
@@ -37,14 +42,22 @@ export type AvatarProps = React.HTMLAttributes<HTMLDivElement> & {
   bgColor?: string
 } & RecipeVariantProps<typeof avatar>
 
-export const Avatar = ({ name, bgColor, context, ...props }: AvatarProps) => {
+export const Avatar = ({
+  name,
+  bgColor,
+  context,
+  notification,
+  style,
+  ...props
+}: AvatarProps) => {
   const initial = name?.trim()?.charAt(0) || ''
   return (
     <div
       style={{
         backgroundColor: bgColor,
+        ...style,
       }}
-      className={avatar({ context })}
+      className={avatar({ context, notification })}
       {...props}
     >
       {initial}