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/site/layout-logged.php

@@ -74,6 +74,11 @@
                   Cennik
                 </a>
               </li>
+              <li>
+                <a href="/apanel/calendar/">
+                  Kalendarz
+                </a>
+              </li>
               <li>
                 <a href="/apanel/settings/">
                   Ustawienia
@@ -139,4 +144,4 @@
   </script>
 </body>
 
-</html>
+</html>