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/daysToWeeks.js

@@ -0,0 +1,32 @@
+import { daysInWeek } from "./constants.js";
+
+/**
+ * @name daysToWeeks
+ * @category Conversion Helpers
+ * @summary Convert days to weeks.
+ *
+ * @description
+ * Convert a number of days to a full number of weeks.
+ *
+ * @param days - The number of days to be converted
+ *
+ * @returns The number of days converted in weeks
+ *
+ * @example
+ * // Convert 14 days to weeks:
+ * const result = daysToWeeks(14)
+ * //=> 2
+ *
+ * @example
+ * // It uses trunc rounding:
+ * const result = daysToWeeks(13)
+ * //=> 1
+ */
+export function daysToWeeks(days) {
+  const result = Math.trunc(days / daysInWeek);
+  // Prevent negative zero
+  return result === 0 ? 0 : result;
+}
+
+// Fallback for modularized imports:
+export default daysToWeeks;