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/utils.d.cts

@@ -0,0 +1,33 @@
+import type { LocaleDayPeriod } from "../../locale/types.js";
+import type { ParseResult } from "./types.js";
+export declare function mapValue<TInput, TResult>(
+  parseFnResult: ParseResult<TInput>,
+  mapFn: (value: TInput) => TResult,
+): ParseResult<TResult>;
+export declare function parseNumericPattern(
+  pattern: RegExp,
+  dateString: string,
+): ParseResult<number>;
+export declare function parseTimezonePattern(
+  pattern: RegExp,
+  dateString: string,
+): ParseResult<number>;
+export declare function parseAnyDigitsSigned(
+  dateString: string,
+): ParseResult<number>;
+export declare function parseNDigits(
+  n: number,
+  dateString: string,
+): ParseResult<number>;
+export declare function parseNDigitsSigned(
+  n: number,
+  dateString: string,
+): ParseResult<number>;
+export declare function dayPeriodEnumToHours(
+  dayPeriod: LocaleDayPeriod,
+): number;
+export declare function normalizeTwoDigitYear(
+  twoDigitYear: number,
+  currentYear: number,
+): number;
+export declare function isLeapYearIndex(year: number): boolean;