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/fromUnixTime.d.ts

@@ -0,0 +1,30 @@
+import type { ContextOptions } from "./types.js";
+/**
+ * The {@link fromUnixTime} function options.
+ */
+export interface FromUnixTimeOptions<DateType extends Date = Date>
+  extends ContextOptions<DateType> {}
+/**
+ * @name fromUnixTime
+ * @category Timestamp Helpers
+ * @summary Create a date from a Unix timestamp.
+ *
+ * @description
+ * Create a date from a Unix timestamp (in seconds). Decimal values will be discarded.
+ *
+ * @param unixTime - The given Unix timestamp (in seconds)
+ * @param options - An object with options. Allows to pass a context.
+ *
+ * @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).
+ *
+ * @returns The date
+ *
+ * @example
+ * // Create the date 29 February 2012 11:45:05:
+ * const result = fromUnixTime(1330515905)
+ * //=> Wed Feb 29 2012 11:45:05
+ */
+export declare function fromUnixTime<DateType extends Date = Date>(
+  unixTime: number,
+  options?: FromUnixTimeOptions<DateType> | undefined,
+): DateType;