Link bar: four digits of message age are enough (the link is dead after 5 s)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

lib/main.dart

@@ -202,8 +202,8 @@ class LinkBar extends StatelessWidget {
     final age = b.lastMessage == null
         ? pad('—', 4)
         : pad(
-            '${DateTime.now().difference(b.lastMessage!).inMilliseconds.clamp(0, 99999)}',
+            '${DateTime.now().difference(b.lastMessage!).inMilliseconds.clamp(0, 9999)}',
-            5,
+            4,
           );
     final offset = b.clockOffset == null
         ? pad('—', 6)