Add visual worker calendar and floating lunch break system

- Monthly calendar grid per worker with colour-coded day status
- Override types: vacation, sick, custom hours, other, day-off
- Date-range override support via modal
- Floating 30-min lunch break: finds slot closest to preferred time
  within configurable window, adapts to existing bookings
- Lunch break only applies for shifts >= 6 hours
- Lunch slot shown in admin calendar; blocked in booking availability
- DB migrations: absence_type/note on worker_schedule_overrides,
  lunch_window_start/end/preferred_time on workers

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

application/views/admin/includes/workers-form.php

@@ -23,6 +23,7 @@
                         <tr>
                             <td>
                                 <a href="<?php echo SITEURL;?>workers/update-worker/<?php echo $resultItem->worker_id;?>"><i class="fas fa-edit"></i></a>
+                                | <a href="<?php echo SITEURL;?>workers/worker-calendar/<?php echo $resultItem->worker_id;?>"><i class="fas fa-calendar-alt"></i></a>
                                 | <a href="<?php echo site_url().'workers/worker-process?delete-worker='.$resultItem->worker_id;?>"  onclick="return confirm('Valóban törölni szeretnéd?');"><i class="fas fa-trash-alt" style="font-size: 14px;color:#585858;"></i></a>
                             </td>
                             <td>#<?php echo $resultItem->worker_id;?></td>