style: enhance layout and functionality of duty markers and calendar

- Updated CSS for `.day` and `.access-denied` to improve layout and visual consistency.
- Introduced a new function `dutyOverlapsLocalRange` in `dateUtils.js` to check duty overlaps within a specified date range.
- Refactored `dutyItemHtml` in `dutyList.js` to utilize `formatTimeLocal` for time formatting, enhancing readability.
- Added utility functions in `hints.js` for parsing duty marker data and building time prefixes, streamlining hint rendering logic.
- Improved the `showAccessDenied` function in `ui.js` to display detailed server messages when access is denied.

webapp/js/dateUtils.js

@@ -29,6 +29,23 @@ export function dutyOverlapsLocalDay(d, dateKey) {
   return end > dayStart && start < dayEnd;
 }
 
+/**
+ * True if duty overlaps any local day in the range [firstKey, lastKey] (inclusive).
+ * @param {object} d - Duty with start_at, end_at
+ * @param {string} firstKey - YYYY-MM-DD (first day of range)
+ * @param {string} lastKey - YYYY-MM-DD (last day of range)
+ * @returns {boolean}
+ */
+export function dutyOverlapsLocalRange(d, firstKey, lastKey) {
+  const [y1, m1, day1] = firstKey.split("-").map(Number);
+  const [y2, m2, day2] = lastKey.split("-").map(Number);
+  const rangeStart = new Date(y1, m1 - 1, day1, 0, 0, 0, 0);
+  const rangeEnd = new Date(y2, m2 - 1, day2, 23, 59, 59, 999);
+  const start = new Date(d.start_at);
+  const end = new Date(d.end_at);
+  return end > rangeStart && start < rangeEnd;
+}
+
 /** @param {Date} d - Date */
 export function firstDayOfMonth(d) {
   return new Date(d.getFullYear(), d.getMonth(), 1);