fix(activity): address code review feedback and improve timeline UX

- Extract shared timeAgo utility, remove duplicates from comment-card and issue-detail
- Remove unused replies prop from CommentCard
- Fix recursive delete to remove all descendant replies, not just direct children
- Improve formatActivity with human-readable status/priority labels and actor names
- Validate parent comment exists and belongs to same issue before creating reply
- Add priority_changed activity recording in activity listeners
- Fix activity SQL query to sort ASC (was DESC, then re-sorted in handler)
- Fix reply-input layout alignment and test submit button selector
- Minor: .gitignore additions, button dark mode aria-expanded fix

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/shared/utils.ts

@@ -0,0 +1,10 @@
+export function timeAgo(dateStr: string): string {
+  const diff = Date.now() - new Date(dateStr).getTime();
+  const minutes = Math.floor(diff / 60000);
+  if (minutes < 1) return "just now";
+  if (minutes < 60) return `${minutes}m ago`;
+  const hours = Math.floor(minutes / 60);
+  if (hours < 24) return `${hours}h ago`;
+  const days = Math.floor(hours / 24);
+  return `${days}d ago`;
+}