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/detect-libc/lib/process.js

@@ -0,0 +1,24 @@
+// Copyright 2017 Lovell Fuller and others.
+// SPDX-License-Identifier: Apache-2.0
+
+'use strict';
+
+const isLinux = () => process.platform === 'linux';
+
+let report = null;
+const getReport = () => {
+  if (!report) {
+    /* istanbul ignore next */
+    if (isLinux() && process.report) {
+      const orig = process.report.excludeNetwork;
+      process.report.excludeNetwork = true;
+      report = process.report.getReport();
+      process.report.excludeNetwork = orig;
+    } else {
+      report = {};
+    }
+  }
+  return report;
+};
+
+module.exports = { isLinux, getReport };