refactor: clean up CSS styles and enhance JavaScript functionality

- Removed outdated CSS styles related to the calendar sticky behavior and duty item animations to streamline the stylesheet.
- Added a reflow trigger in the JavaScript function to ensure proper rendering of the day detail panel when opened, improving user experience.
- Enhanced overall code clarity by eliminating unnecessary styles and improving the animation handling logic.

webapp/js/dayDetail.js

@@ -186,6 +186,8 @@ function showAsBottomSheet() {
 
   requestAnimationFrame(() => {
     requestAnimationFrame(() => {
+      // Force reflow so WebView paints the "closed" state before we add --open
+      void panelEl.offsetHeight;
       overlayEl.classList.add("day-detail-overlay--visible");
       panelEl.classList.add("day-detail-panel--open");
       const closeBtn = panelEl.querySelector(".day-detail-close");