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/enhanced-resolve/lib/ConditionalPlugin.js

@@ -0,0 +1,59 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Tobias Koppers @sokra
+*/
+
+"use strict";
+
+/** @typedef {import("./Resolver")} Resolver */
+/** @typedef {import("./Resolver").ResolveRequest} ResolveRequest */
+/** @typedef {import("./Resolver").ResolveStepHook} ResolveStepHook */
+
+module.exports = class ConditionalPlugin {
+	/**
+	 * @param {string | ResolveStepHook} source source
+	 * @param {Partial<ResolveRequest>} test compare object
+	 * @param {string | null} message log message
+	 * @param {boolean} allowAlternatives when false, do not continue with the current step when "test" matches
+	 * @param {string | ResolveStepHook} target target
+	 */
+	constructor(source, test, message, allowAlternatives, target) {
+		this.source = source;
+		this.test = test;
+		this.message = message;
+		this.allowAlternatives = allowAlternatives;
+		this.target = target;
+	}
+
+	/**
+	 * @param {Resolver} resolver the resolver
+	 * @returns {void}
+	 */
+	apply(resolver) {
+		const target = resolver.ensureHook(this.target);
+		const { test, message, allowAlternatives } = this;
+		const keys = /** @type {(keyof ResolveRequest)[]} */ (Object.keys(test));
+		resolver
+			.getHook(this.source)
+			.tapAsync("ConditionalPlugin", (request, resolveContext, callback) => {
+				for (const prop of keys) {
+					if (request[prop] !== test[prop]) return callback();
+				}
+				resolver.doResolve(
+					target,
+					request,
+					message,
+					resolveContext,
+					allowAlternatives
+						? callback
+						: (err, result) => {
+								if (err) return callback(err);
+
+								// Don't allow other alternatives
+								if (result === undefined) return callback(null, null);
+								callback(null, result);
+							},
+				);
+			});
+	}
+};