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/ui.js

@@ -16,7 +16,7 @@ import {
 
 /**
  * Show access-denied view and hide calendar/list/loading/error.
- * @param {string} [serverDetail] - message from API 403 detail (unused; kept for callers)
+ * @param {string} [serverDetail] - message from API 403 detail (shown below main text when present)
  */
 export function showAccessDenied(serverDetail) {
   if (headerEl) headerEl.hidden = true;
@@ -25,7 +25,16 @@ export function showAccessDenied(serverDetail) {
   if (dutyListEl) dutyListEl.hidden = true;
   if (loadingEl) loadingEl.classList.add("hidden");
   if (errorEl) errorEl.hidden = true;
-  if (accessDeniedEl) accessDeniedEl.hidden = false;
+  if (accessDeniedEl) {
+    accessDeniedEl.innerHTML = "<p>Доступ запрещён.</p>";
+    if (serverDetail && serverDetail.trim()) {
+      const detail = document.createElement("p");
+      detail.className = "access-denied-detail";
+      detail.textContent = serverDetail;
+      accessDeniedEl.appendChild(detail);
+    }
+    accessDeniedEl.hidden = false;
+  }
 }
 
 /**