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/locale/nl.js

@@ -0,0 +1,33 @@
+import { formatDistance } from "./nl/_lib/formatDistance.js";
+import { formatLong } from "./nl/_lib/formatLong.js";
+import { formatRelative } from "./nl/_lib/formatRelative.js";
+import { localize } from "./nl/_lib/localize.js";
+import { match } from "./nl/_lib/match.js";
+
+/**
+ * @category Locales
+ * @summary Dutch locale.
+ * @language Dutch
+ * @iso-639-2 nld
+ * @author Jorik Tangelder [@jtangelder](https://github.com/jtangelder)
+ * @author Ruben Stolk [@rubenstolk](https://github.com/rubenstolk)
+ * @author Lode Vanhove [@bitcrumb](https://github.com/bitcrumb)
+ * @author Edo Rivai [@edorivai](https://github.com/edorivai)
+ * @author Niels Keurentjes [@curry684](https://github.com/curry684)
+ * @author Stefan Vermaas [@stefanvermaas](https://github.com/stefanvermaas)
+ */
+export const nl = {
+  code: "nl",
+  formatDistance: formatDistance,
+  formatLong: formatLong,
+  formatRelative: formatRelative,
+  localize: localize,
+  match: match,
+  options: {
+    weekStartsOn: 1 /* Monday */,
+    firstWeekContainsDate: 4,
+  },
+};
+
+// Fallback for modularized imports:
+export default nl;