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/index.d.ts

@@ -0,0 +1,14 @@
+// Copyright 2017 Lovell Fuller and others.
+// SPDX-License-Identifier: Apache-2.0
+
+export const GLIBC: 'glibc';
+export const MUSL: 'musl';
+
+export function family(): Promise<string | null>;
+export function familySync(): string | null;
+
+export function isNonGlibcLinux(): Promise<boolean>;
+export function isNonGlibcLinuxSync(): boolean;
+
+export function version(): Promise<string | null>;
+export function versionSync(): string | null;