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/rollup/dist/loadConfigFile.d.ts

@@ -0,0 +1,20 @@
+import type { LogHandler, MergedRollupOptions, RollupLog } from './rollup';
+
+export interface BatchWarnings {
+	add: (warning: RollupLog) => void;
+	readonly count: number;
+	flush: () => void;
+	log: LogHandler;
+	readonly warningOccurred: boolean;
+}
+
+export type LoadConfigFile = typeof loadConfigFile;
+
+export function loadConfigFile(
+	fileName: string,
+	commandOptions: any,
+	watchMode?: boolean
+): Promise<{
+	options: MergedRollupOptions[];
+	warnings: BatchWarnings;
+}>;