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/addMilliseconds.cjs

@@ -0,0 +1,37 @@
+"use strict";
+exports.addMilliseconds = addMilliseconds;
+var _index = require("./constructFrom.cjs");
+var _index2 = require("./toDate.cjs");
+
+/**
+ * The {@link addMilliseconds} function options.
+ */
+
+/**
+ * @name addMilliseconds
+ * @category Millisecond Helpers
+ * @summary Add the specified number of milliseconds to the given date.
+ *
+ * @description
+ * Add the specified number of milliseconds to the given date.
+ *
+ * @typeParam DateType - The `Date` type, the function operates on. Gets inferred from passed arguments. Allows to use extensions like [`UTCDate`](https://github.com/date-fns/utc).
+ * @typeParam ResultDate - The result `Date` type, it is the type returned from the context function if it is passed, or inferred from the arguments.
+ *
+ * @param date - The date to be changed
+ * @param amount - The amount of milliseconds to be added.
+ * @param options - The options object
+ *
+ * @returns The new date with the milliseconds added
+ *
+ * @example
+ * // Add 750 milliseconds to 10 July 2014 12:45:30.000:
+ * const result = addMilliseconds(new Date(2014, 6, 10, 12, 45, 30, 0), 750)
+ * //=> Thu Jul 10 2014 12:45:30.750
+ */
+function addMilliseconds(date, amount, options) {
+  return (0, _index.constructFrom)(
+    options?.in || date,
+    +(0, _index2.toDate)(date) + amount,
+  );
+}