Add swipe navigation for calendar month view

- Implemented touch event listeners to allow users to swipe left or right on the calendar for month navigation.
- Added a swipe threshold to prevent accidental navigation and ensure smooth user experience.
- Updated CSS to enable touch actions for better responsiveness on touch devices.

webapp/style.css

@@ -80,6 +80,7 @@ body {
   background: var(--bg);
   padding-bottom: 12px;
   margin-bottom: 4px;
+  touch-action: pan-y;
 }
 
 .calendar-sticky.is-scrolled {