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/dutyList.js

@@ -13,7 +13,6 @@ import {
   formatTimeLocal,
   formatDateKey
 } from "./dateUtils.js";
-import { dutiesByDate } from "./calendar.js";
 
 /**
  * Build HTML for one timeline duty card: one-day "DD.MM, HH:MM – HH:MM" or multi-day.
@@ -60,8 +59,6 @@ export function dutyTimelineCardHtml(d, isCurrent) {
  * @returns {string}
  */
 export function dutyItemHtml(d, typeLabelOverride, showUntilEnd, extraClass) {
-  const startDate = new Date(d.start_at);
-  const endDate = new Date(d.end_at);
   const typeLabel =
     typeLabelOverride != null
       ? typeLabelOverride
@@ -70,25 +67,14 @@ export function dutyItemHtml(d, typeLabelOverride, showUntilEnd, extraClass) {
   if (extraClass) itemClass += " " + extraClass;
   let timeOrRange = "";
   if (showUntilEnd && d.event_type === "duty") {
-    const end =
-      String(endDate.getHours()).padStart(2, "0") +
-      ":" +
-      String(endDate.getMinutes()).padStart(2, "0");
-    timeOrRange = "до " + end;
+    timeOrRange = "до " + formatTimeLocal(d.end_at);
   } else if (d.event_type === "vacation" || d.event_type === "unavailable") {
     const startStr = formatDateKey(d.start_at);
     const endStr = formatDateKey(d.end_at);
     timeOrRange = startStr === endStr ? startStr : startStr + " – " + endStr;
   } else {
-    const start =
-      String(startDate.getHours()).padStart(2, "0") +
-      ":" +
-      String(startDate.getMinutes()).padStart(2, "0");
-    const end =
-      String(endDate.getHours()).padStart(2, "0") +
-      ":" +
-      String(endDate.getMinutes()).padStart(2, "0");
-    timeOrRange = start + " – " + end;
+    timeOrRange =
+      formatTimeLocal(d.start_at) + " – " + formatTimeLocal(d.end_at);
   }
   return (
     '<div class="' +