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/zh-HK.js

@@ -0,0 +1,28 @@
+import { formatDistance } from "./zh-HK/_lib/formatDistance.js";
+import { formatLong } from "./zh-HK/_lib/formatLong.js";
+import { formatRelative } from "./zh-HK/_lib/formatRelative.js";
+import { localize } from "./zh-HK/_lib/localize.js";
+import { match } from "./zh-HK/_lib/match.js";
+
+/**
+ * @category Locales
+ * @summary Chinese Traditional locale.
+ * @language Chinese Traditional
+ * @iso-639-2 zho
+ * @author Gary Ip [@gaplo](https://github.com/gaplo)
+ */
+export const zhHK = {
+  code: "zh-HK",
+  formatDistance: formatDistance,
+  formatLong: formatLong,
+  formatRelative: formatRelative,
+  localize: localize,
+  match: match,
+  options: {
+    weekStartsOn: 0 /* Sunday */,
+    firstWeekContainsDate: 1,
+  },
+};
+
+// Fallback for modularized imports:
+export default zhHK;