feat: enhance CI workflow and update webapp styles

- Added Node.js setup and webapp testing steps to the CI workflow for improved integration.
- Updated HTML to link multiple CSS files for better modularity and organization of styles.
- Removed deprecated `style.css` and introduced new CSS files for base styles, calendar, day detail, hints, markers, states, and duty list to enhance maintainability and readability.
- Implemented new styles for improved presentation of duty information and user interactions.
- Added unit tests for new API functions and contact link rendering to ensure functionality and reliability.

webapp/js/ui.js

@@ -4,15 +4,15 @@
 
 import {
   state,
-  calendarEl,
-  dutyListEl,
-  loadingEl,
-  errorEl,
-  accessDeniedEl,
-  headerEl,
-  weekdaysEl,
-  prevBtn,
-  nextBtn
+  getCalendarEl,
+  getDutyListEl,
+  getLoadingEl,
+  getErrorEl,
+  getAccessDeniedEl,
+  getHeaderEl,
+  getWeekdaysEl,
+  getPrevBtn,
+  getNextBtn
 } from "./dom.js";
 import { t } from "./i18n.js";
 
@@ -21,6 +21,13 @@ import { t } from "./i18n.js";
  * @param {string} [serverDetail] - message from API 403 detail (shown below main text when present)
  */
 export function showAccessDenied(serverDetail) {
+  const headerEl = getHeaderEl();
+  const weekdaysEl = getWeekdaysEl();
+  const calendarEl = getCalendarEl();
+  const dutyListEl = getDutyListEl();
+  const loadingEl = getLoadingEl();
+  const errorEl = getErrorEl();
+  const accessDeniedEl = getAccessDeniedEl();
   if (headerEl) headerEl.hidden = true;
   if (weekdaysEl) weekdaysEl.hidden = true;
   if (calendarEl) calendarEl.hidden = true;
@@ -44,6 +51,11 @@ export function showAccessDenied(serverDetail) {
  * Hide access-denied and show calendar/list/header/weekdays.
  */
 export function hideAccessDenied() {
+  const accessDeniedEl = getAccessDeniedEl();
+  const headerEl = getHeaderEl();
+  const weekdaysEl = getWeekdaysEl();
+  const calendarEl = getCalendarEl();
+  const dutyListEl = getDutyListEl();
   if (accessDeniedEl) accessDeniedEl.hidden = true;
   if (headerEl) headerEl.hidden = false;
   if (weekdaysEl) weekdaysEl.hidden = false;
@@ -56,6 +68,8 @@ export function hideAccessDenied() {
  * @param {string} msg - Error text
  */
 export function showError(msg) {
+  const errorEl = getErrorEl();
+  const loadingEl = getLoadingEl();
   if (errorEl) {
     errorEl.textContent = msg;
     errorEl.hidden = false;
@@ -68,6 +82,8 @@ export function showError(msg) {
  * @param {boolean} enabled
  */
 export function setNavEnabled(enabled) {
+  const prevBtn = getPrevBtn();
+  const nextBtn = getNextBtn();
   if (prevBtn) prevBtn.disabled = !enabled;
   if (nextBtn) nextBtn.disabled = !enabled;
 }