feat: implement day detail panel for calendar

- Introduced a new `dayDetail.js` module to manage the day detail panel functionality, allowing users to view detailed information about duties and events for each calendar day.
- Enhanced the calendar rendering in `calendar.js` to include visual indicators for duties and events, improving user interaction and experience.
- Updated CSS in `style.css` to style the day detail panel and its components, ensuring a responsive design for both desktop and mobile views.
- Refactored `hints.js` to export the `getDutyMarkerRows` function, facilitating better integration with the new day detail features.
- Added localization support for the day detail panel in `i18n.js`, including new translations for close button and event titles.
- Enhanced the initialization process in `main.js` to set up the day detail panel on application load.

webapp/js/hints.js

@@ -132,7 +132,7 @@ function buildDutyItemTimePrefix(item, idx, total, hintDay, sep, fromLabel, toLa
  * @param {string} toLabel
  * @returns {{ timePrefix: string, fullName: string }[]}
  */
-function getDutyMarkerRows(dutyItems, hintDay, timeSep, fromLabel, toLabel) {
+export function getDutyMarkerRows(dutyItems, hintDay, timeSep, fromLabel, toLabel) {
   return dutyItems.map((item, idx) => {
     const timePrefix = buildDutyItemTimePrefix(
       item,