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/differenceInCalendarQuarters.cjs

@@ -0,0 +1,44 @@
+"use strict";
+exports.differenceInCalendarQuarters = differenceInCalendarQuarters;
+var _index = require("./_lib/normalizeDates.cjs");
+var _index2 = require("./getQuarter.cjs");
+
+/**
+ * The {@link differenceInCalendarQuarters} function options.
+ */
+
+/**
+ * @name differenceInCalendarQuarters
+ * @category Quarter Helpers
+ * @summary Get the number of calendar quarters between the given dates.
+ *
+ * @description
+ * Get the number of calendar quarters between the given dates.
+ *
+ * @param laterDate - The later date
+ * @param earlierDate - The earlier date
+ * @param options - An object with options
+ *
+ * @returns The number of calendar quarters
+ *
+ * @example
+ * // How many calendar quarters are between 31 December 2013 and 2 July 2014?
+ * const result = differenceInCalendarQuarters(
+ *   new Date(2014, 6, 2),
+ *   new Date(2013, 11, 31)
+ * )
+ * //=> 3
+ */
+function differenceInCalendarQuarters(laterDate, earlierDate, options) {
+  const [laterDate_, earlierDate_] = (0, _index.normalizeDates)(
+    options?.in,
+    laterDate,
+    earlierDate,
+  );
+
+  const yearsDiff = laterDate_.getFullYear() - earlierDate_.getFullYear();
+  const quartersDiff =
+    (0, _index2.getQuarter)(laterDate_) - (0, _index2.getQuarter)(earlierDate_);
+
+  return yearsDiff * 4 + quartersDiff;
+}