Add comment skeleton loaders, workflow validation, monthly schedule fix

- TicketView.php: Show 3 lt-skeleton-card placeholders in the comment list
  while "Load more" fetches; skeletons are removed on resolve or error
- ticket.css: Add .comment-skeleton margin spacing
- WorkflowDesignerView.php + manage_workflows.php: Prevent creating/editing
  status transitions where from_status === to_status (client + server check)
- RecurringTicketsView.php: Expand monthly day picker from 28 to 31 days
  (days 29-31 labelled "last day in short months")
- RecurringTicketModel.php: Clamp monthly schedule day to last day of target
  month using format('t') instead of hard-capping at 28

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

models/RecurringTicketModel.php

@@ -181,10 +181,13 @@ class RecurringTicketModel {
                 break;
 
             case 'monthly':
-                $day = max(1, min(28, $scheduleDay)); // Limit to 28 for safety
+                $day = max(1, min(31, $scheduleDay));
                 $next = new DateTime();
                 $next->modify('first day of next month');
-                $next->setDate($next->format('Y'), $next->format('m'), $day);
+                // Clamp to the last day of the target month (handles Feb, 30-day months, etc.)
+                $daysInMonth = (int)$next->format('t');
+                $day = min($day, $daysInMonth);
+                $next->setDate((int)$next->format('Y'), (int)$next->format('m'), $day);
                 $next->setTime($time->format('H'), $time->format('i'), 0);
                 break;