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/style.css

@@ -143,6 +143,7 @@ body {
 }
 
 .day {
+  position: relative;
   aspect-ratio: 1;
   display: flex;
   flex-direction: column;
@@ -175,10 +176,6 @@ body {
   border: 1px solid color-mix(in srgb, var(--today) 35%, transparent);
 }
 
-.day {
-  position: relative;
-}
-
 .info-btn {
   position: absolute;
   top: 0;
@@ -577,6 +574,12 @@ body {
   font-weight: 600;
 }
 
+.access-denied .access-denied-detail {
+  margin-top: 8px;
+  font-size: 0.9rem;
+  color: var(--muted);
+}
+
 .access-denied[hidden] {
   display: none !important;
 }