feat: add calendar subscription token functionality and ICS generation

- Introduced a new database model for calendar subscription tokens, allowing users to generate unique tokens for accessing their personal calendar.
- Implemented API endpoint to return ICS files containing only the subscribing user's duties, enhancing user experience with personalized calendar access.
- Added utility functions for generating ICS files from user duties, ensuring proper formatting and timezone handling.
- Updated command handlers to support the new calendar link feature, providing users with easy access to their personal calendar subscriptions.
- Included unit tests for the new functionality, ensuring reliability and correctness of token generation and ICS file creation.

webapp/js/dayDetail.js

@@ -91,25 +91,27 @@ export function buildDayDetailContent(dateKey, duties, eventSummaries) {
   }
 
   if (unavailableList.length > 0) {
+    const uniqueUnavailable = [...new Set(unavailableList.map((d) => d.full_name || "").filter(Boolean))];
     html +=
       '<section class="day-detail-section day-detail-section--unavailable">' +
       '<h3 class="day-detail-section-title">' +
       escapeHtml(t(lang, "event_type.unavailable")) +
       "</h3><ul class=\"day-detail-list\">";
-    unavailableList.forEach((d) => {
-      html += "<li>" + escapeHtml(d.full_name || "") + "</li>";
+    uniqueUnavailable.forEach((name) => {
+      html += "<li>" + escapeHtml(name) + "</li>";
     });
     html += "</ul></section>";
   }
 
   if (vacationList.length > 0) {
+    const uniqueVacation = [...new Set(vacationList.map((d) => d.full_name || "").filter(Boolean))];
     html +=
       '<section class="day-detail-section day-detail-section--vacation">' +
       '<h3 class="day-detail-section-title">' +
       escapeHtml(t(lang, "event_type.vacation")) +
       "</h3><ul class=\"day-detail-list\">";
-    vacationList.forEach((d) => {
-      html += "<li>" + escapeHtml(d.full_name || "") + "</li>";
+    uniqueVacation.forEach((name) => {
+      html += "<li>" + escapeHtml(name) + "</li>";
     });
     html += "</ul></section>";
   }