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/parsers/ExtendedYearParser.js

@@ -0,0 +1,23 @@
+import { Parser } from "../Parser.js";
+
+import { parseNDigitsSigned } from "../utils.js";
+
+export class ExtendedYearParser extends Parser {
+  priority = 130;
+
+  parse(dateString, token) {
+    if (token === "u") {
+      return parseNDigitsSigned(4, dateString);
+    }
+
+    return parseNDigitsSigned(token.length, dateString);
+  }
+
+  set(date, _flags, value) {
+    date.setFullYear(value, 0, 1);
+    date.setHours(0, 0, 0, 0);
+    return date;
+  }
+
+  incompatibleTokens = ["G", "y", "Y", "R", "w", "I", "i", "e", "c", "t", "T"];
+}