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/parse/_lib/constants.d.ts

@@ -0,0 +1,28 @@
+export declare const numericPatterns: {
+  month: RegExp;
+  date: RegExp;
+  dayOfYear: RegExp;
+  week: RegExp;
+  hour23h: RegExp;
+  hour24h: RegExp;
+  hour11h: RegExp;
+  hour12h: RegExp;
+  minute: RegExp;
+  second: RegExp;
+  singleDigit: RegExp;
+  twoDigits: RegExp;
+  threeDigits: RegExp;
+  fourDigits: RegExp;
+  anyDigitsSigned: RegExp;
+  singleDigitSigned: RegExp;
+  twoDigitsSigned: RegExp;
+  threeDigitsSigned: RegExp;
+  fourDigitsSigned: RegExp;
+};
+export declare const timezonePatterns: {
+  basicOptionalMinutes: RegExp;
+  basic: RegExp;
+  basicOptionalSeconds: RegExp;
+  extended: RegExp;
+  extendedOptionalSeconds: RegExp;
+};