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/tapable/lib/util-browser.js

@@ -0,0 +1,18 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Tobias Koppers @sokra
+*/
+"use strict";
+
+module.exports.deprecate = (fn, msg) => {
+	let once = true;
+	return function deprecate() {
+		if (once) {
+			// eslint-disable-next-line no-console
+			console.warn(`DeprecationWarning: ${msg}`);
+			once = false;
+		}
+		// eslint-disable-next-line prefer-rest-params
+		return fn.apply(this, arguments);
+	};
+};