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/main.js

@@ -26,7 +26,8 @@ import {
   firstDayOfMonth,
   lastDayOfMonth,
   getMonday,
-  localDateString
+  localDateString,
+  dutyOverlapsLocalRange
 } from "./dateUtils.js";
 
 initTheme();
@@ -113,12 +114,9 @@ async function loadMonth() {
     const last = lastDayOfMonth(current);
     const firstKey = localDateString(first);
     const lastKey = localDateString(last);
-    const dutiesInMonth = duties.filter((d) => {
-      const byDateLocal = dutiesByDate([d]);
-      return Object.keys(byDateLocal).some(
-        (key) => key >= firstKey && key <= lastKey
-      );
-    });
+    const dutiesInMonth = duties.filter((d) =>
+      dutyOverlapsLocalRange(d, firstKey, lastKey)
+    );
     state.lastDutiesForList = dutiesInMonth;
     renderDutyList(dutiesInMonth);
     if (state.todayRefreshInterval) {
@@ -197,16 +195,17 @@ if (nextBtn) {
     (e) => {
       if (e.changedTouches.length === 0) return;
       if (accessDeniedEl && !accessDeniedEl.hidden) return;
-      if (prevBtn && prevBtn.disabled) return;
       const t = e.changedTouches[0];
       const deltaX = t.clientX - startX;
       const deltaY = t.clientY - startY;
       if (Math.abs(deltaX) <= SWIPE_THRESHOLD) return;
       if (Math.abs(deltaY) > Math.abs(deltaX)) return;
       if (deltaX > SWIPE_THRESHOLD) {
+        if (prevBtn && prevBtn.disabled) return;
         state.current.setMonth(state.current.getMonth() - 1);
         loadMonth();
       } else if (deltaX < -SWIPE_THRESHOLD) {
+        if (nextBtn && nextBtn.disabled) return;
         state.current.setMonth(state.current.getMonth() + 1);
         loadMonth();
       }