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/date-fns/locale/_lib/buildMatchPatternFn.js

@@ -0,0 +1,20 @@
+export function buildMatchPatternFn(args) {
+  return (string, options = {}) => {
+    const matchResult = string.match(args.matchPattern);
+    if (!matchResult) return null;
+    const matchedString = matchResult[0];
+
+    const parseResult = string.match(args.parsePattern);
+    if (!parseResult) return null;
+    let value = args.valueCallback
+      ? args.valueCallback(parseResult[0])
+      : parseResult[0];
+
+    // [TODO] I challenge you to fix the type
+    value = options.valueCallback ? options.valueCallback(value) : value;
+
+    const rest = string.slice(matchedString.length);
+
+    return { value, rest };
+  };
+}