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/app.js

@@ -536,6 +536,37 @@
     loadMonth();
   });
 
+  (function bindSwipeMonth() {
+    var swipeEl = document.getElementById("calendarSticky");
+    if (!swipeEl) return;
+    var startX = 0;
+    var startY = 0;
+    var SWIPE_THRESHOLD = 50;
+    swipeEl.addEventListener("touchstart", function (e) {
+      if (e.changedTouches.length === 0) return;
+      var t = e.changedTouches[0];
+      startX = t.clientX;
+      startY = t.clientY;
+    }, { passive: true });
+    swipeEl.addEventListener("touchend", function (e) {
+      if (e.changedTouches.length === 0) return;
+      if (!accessDeniedEl.hidden) return;
+      if (prevBtn.disabled) return;
+      var t = e.changedTouches[0];
+      var deltaX = t.clientX - startX;
+      var deltaY = t.clientY - startY;
+      if (Math.abs(deltaX) <= SWIPE_THRESHOLD) return;
+      if (Math.abs(deltaY) > Math.abs(deltaX)) return;
+      if (deltaX > SWIPE_THRESHOLD) {
+        current.setMonth(current.getMonth() - 1);
+        loadMonth();
+      } else if (deltaX < -SWIPE_THRESHOLD) {
+        current.setMonth(current.getMonth() + 1);
+        loadMonth();
+      }
+    }, { passive: true });
+  })();
+
   function bindStickyScrollShadow() {
     var stickyEl = document.getElementById("calendarSticky");
     if (!stickyEl || document._stickyScrollBound) return;

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 {