feat: implement day detail panel for calendar

- Introduced a new `dayDetail.js` module to manage the day detail panel functionality, allowing users to view detailed information about duties and events for each calendar day.
- Enhanced the calendar rendering in `calendar.js` to include visual indicators for duties and events, improving user interaction and experience.
- Updated CSS in `style.css` to style the day detail panel and its components, ensuring a responsive design for both desktop and mobile views.
- Refactored `hints.js` to export the `getDutyMarkerRows` function, facilitating better integration with the new day detail features.
- Added localization support for the day detail panel in `i18n.js`, including new translations for close button and event titles.
- Enhanced the initialization process in `main.js` to set up the day detail panel on application load.

webapp/style.css

@@ -176,6 +176,149 @@ body {
   border: 1px solid color-mix(in srgb, var(--today) 35%, transparent);
 }
 
+.day {
+  cursor: pointer;
+}
+
+.day-indicator {
+  display: flex;
+  flex-wrap: wrap;
+  justify-content: center;
+  gap: 2px;
+  margin-top: 2px;
+}
+
+.day-indicator-dot {
+  width: 6px;
+  height: 6px;
+  border-radius: 50%;
+  flex-shrink: 0;
+}
+
+.day-indicator-dot.duty {
+  background: var(--duty);
+}
+
+.day-indicator-dot.unavailable {
+  background: var(--unavailable);
+}
+
+.day-indicator-dot.vacation {
+  background: var(--vacation);
+}
+
+.day-indicator-dot.events {
+  background: var(--accent);
+}
+
+/* === Day detail panel (popover / bottom sheet) */
+.day-detail-overlay {
+  position: fixed;
+  inset: 0;
+  z-index: 999;
+  background: rgba(0, 0, 0, 0.4);
+  -webkit-tap-highlight-color: transparent;
+}
+
+.day-detail-panel {
+  position: fixed;
+  z-index: 1000;
+  max-width: min(360px, calc(100vw - 24px));
+  max-height: 70vh;
+  overflow: auto;
+  background: var(--surface);
+  color: var(--text);
+  border-radius: 12px;
+  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.35);
+  padding: 12px 16px;
+  padding-top: 36px;
+}
+
+.day-detail-panel--sheet {
+  left: 0;
+  right: 0;
+  bottom: 0;
+  top: auto;
+  width: 100%;
+  max-width: none;
+  max-height: 70vh;
+  border-radius: 16px 16px 0 0;
+  padding-top: 12px;
+  padding-left: 16px;
+  padding-right: 16px;
+  padding-bottom: max(16px, env(safe-area-inset-bottom));
+}
+
+.day-detail-panel--sheet::before {
+  content: "";
+  display: block;
+  width: 36px;
+  height: 4px;
+  margin: 0 auto 8px;
+  background: var(--muted);
+  border-radius: 2px;
+}
+
+.day-detail-close {
+  position: absolute;
+  top: 8px;
+  right: 8px;
+  width: 32px;
+  height: 32px;
+  padding: 0;
+  border: none;
+  background: transparent;
+  color: var(--muted);
+  font-size: 1.5rem;
+  line-height: 1;
+  cursor: pointer;
+  border-radius: 8px;
+}
+
+.day-detail-close:hover {
+  color: var(--text);
+  background: color-mix(in srgb, var(--muted) 25%, transparent);
+}
+
+.day-detail-title {
+  margin: 0 0 12px 0;
+  font-size: 1.1rem;
+  font-weight: 600;
+}
+
+.day-detail-sections {
+  display: flex;
+  flex-direction: column;
+  gap: 12px;
+}
+
+.day-detail-section-title {
+  margin: 0 0 4px 0;
+  font-size: 0.8rem;
+  font-weight: 600;
+  color: var(--muted);
+}
+
+.day-detail-section--duty .day-detail-section-title { color: var(--duty); }
+.day-detail-section--unavailable .day-detail-section-title { color: var(--unavailable); }
+.day-detail-section--vacation .day-detail-section-title { color: var(--vacation); }
+.day-detail-section--events .day-detail-section-title { color: var(--accent); }
+
+.day-detail-list {
+  margin: 0;
+  padding-left: 1.2em;
+  font-size: 0.9rem;
+  line-height: 1.45;
+}
+
+.day-detail-list li {
+  margin-bottom: 2px;
+}
+
+.day-detail-time {
+  color: var(--muted);
+}
+
 .info-btn {
   position: absolute;
   top: 0;