feat: enhance day detail panel functionality and user experience

- Added functionality to lock the background scroll when the day detail panel is open, improving user interaction by preventing background movement.
- Implemented logic to restore the scroll position when the panel is closed, ensuring a seamless user experience.
- Updated CSS to support the new behavior, enhancing the visual consistency of the day detail panel.
- Added early return checks in navigation button event listeners to prevent actions while the day detail panel is open, improving performance and usability.

webapp/style.css

@@ -212,6 +212,14 @@ body {
 }
 
 /* === Day detail panel (popover / bottom sheet) */
+/* Блокировка фона при открытом bottom sheet: прокрутка и свайпы отключены */
+body.day-detail-sheet-open {
+  position: fixed;
+  left: 0;
+  right: 0;
+  overflow: hidden;
+}
+
 .day-detail-overlay {
   position: fixed;
   inset: 0;