Add OpenAPI docs, frontend, migrations, and API updates

- OpenAPI: add missing endpoints (add-from-url, subscriptions, public availability)
- OpenAPI: CalendarSubscription schema, Subscriptions tag
- Frontend app
- Migrations: count_for_availability, subscriptions_sync, user_preferences, calendar_settings
- Config, rate limit, auth, calendar, booking, ICS, availability, user service updates

Made-with: Cursor

frontend/node_modules/date-fns/closestIndexTo.js

@@ -0,0 +1,57 @@
+import { toDate } from "./toDate.js";
+
+/**
+ * @name closestIndexTo
+ * @category Common Helpers
+ * @summary Return an index of the closest date from the array comparing to the given date.
+ *
+ * @description
+ * Return an index of the closest date from the array comparing to the given date.
+ *
+ * @param dateToCompare - The date to compare with
+ * @param dates - The array to search
+ *
+ * @returns An index of the date closest to the given date or undefined if no valid value is given
+ *
+ * @example
+ * // Which date is closer to 6 September 2015?
+ * const dateToCompare = new Date(2015, 8, 6)
+ * const datesArray = [
+ *   new Date(2015, 0, 1),
+ *   new Date(2016, 0, 1),
+ *   new Date(2017, 0, 1)
+ * ]
+ * const result = closestIndexTo(dateToCompare, datesArray)
+ * //=> 1
+ */
+export function closestIndexTo(dateToCompare, dates) {
+  // [TODO] It would be better to return -1 here rather than undefined, as this
+  // is how JS behaves, but it would be a breaking change, so we need
+  // to consider it for v4.
+  const timeToCompare = +toDate(dateToCompare);
+
+  if (isNaN(timeToCompare)) return NaN;
+
+  let result;
+  let minDistance;
+  dates.forEach((date, index) => {
+    const date_ = toDate(date);
+
+    if (isNaN(+date_)) {
+      result = NaN;
+      minDistance = NaN;
+      return;
+    }
+
+    const distance = Math.abs(timeToCompare - +date_);
+    if (result == null || distance < minDistance) {
+      result = index;
+      minDistance = distance;
+    }
+  });
+
+  return result;
+}
+
+// Fallback for modularized imports:
+export default closestIndexTo;