feat: redesign tickets main view and basket view with improved styles and layout

- Updated SCSS for tickets main view and basket view, enhancing visual design and responsiveness.
- Added new calendar functionality in the admin panel for managing ticket availability.
- Implemented error handling for ticket availability in the basket view.
- Introduced a new calendar availability table in the database for tracking ticket dates.
- Added a new link to the calendar in the logged-in user navigation.
- Improved ticket selection logic to disable unavailable tickets in the main view.
- Created guidelines for code standards in AGENTS.md.

templates/tickets/basket-view.php

@@ -10,6 +10,14 @@
   }
 ?>
 
+<?php if (!empty($_GET['calendar_error'])) : ?>
+  <div class="container mt-3">
+    <div class="alert alert-danger">
+      Co najmniej jeden bilet jest już niedostępny w wybranym terminie. Zmień datę w koszyku.
+    </div>
+  </div>
+<?php endif; ?>
+
 <div id="basket_page">
   <div class="basket_content">
     <div class="container">
@@ -202,6 +210,15 @@ $(function() {
       },
       success: function(data) {
         response = jQuery.parseJSON(data);
+        if (response.status === 'error') {
+          if ($.alert) {
+            $.alert(response.message);
+          } else {
+            alert(response.message);
+          }
+          return;
+        }
+
         $('.box_01').html(response.basket_form);
         $('.box_02 .basket_summary').html(response.basket_summary);
       }
@@ -296,4 +313,4 @@ $(function() {
     }
   }
 });
-</script>
+</script>