Restyle issue chat comments for chat-like UX

User messages: right-aligned bubbles (85% max-width) with gray
background, no border. Hover reveals short date + copy icon.

Agent messages: borderless with avatar, name, date and three-dots
in header. Left-aligned action bar with icon-only copy, thumbs up,
and thumbs down. Thumbs down opens a floating popover for reason.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

ui/src/lib/utils.ts

@@ -29,6 +29,13 @@ export function formatDateTime(date: Date | string): string {
   });
 }
 
+export function formatShortDate(date: Date | string): string {
+  return new Date(date).toLocaleString("en-US", {
+    month: "short",
+    day: "numeric",
+  });
+}
+
 export function relativeTime(date: Date | string): string {
   const now = Date.now();
   const then = new Date(date).getTime();