Add visual booking calendar (weekly Teams-style view)

- New weekly calendar at /bookings/calendar with time blocks per booking
- Color-coded by worker, overlapping bookings shown side-by-side
- Click booking to see details, edit or delete
- Worker filter dropdown, week navigation (prev/next/today)
- AJAX week loading for smooth navigation
- Link between list view and calendar view

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

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

@@ -2,6 +2,7 @@
     <div class="pageTitle"><?php echo $pageTitle;?></div>
     <div class="form-row">
         <a href="<?php echo SITEURL;?>bookings/add-booking" class="submitBtn">Új foglalás</a>
+        <a href="<?php echo SITEURL;?>bookings/calendar" class="submitBtn">Naptárnézet</a>
     </div>
     <div class="form-row">
         <select id="booking-filter" class="formDropdownBox" style="padding:0">