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/TimestampSecondsParser.cjs

@@ -0,0 +1,24 @@
+"use strict";
+exports.TimestampSecondsParser = void 0;
+var _index = require("../../../constructFrom.cjs");
+var _Parser = require("../Parser.cjs");
+
+var _utils = require("../utils.cjs");
+
+class TimestampSecondsParser extends _Parser.Parser {
+  priority = 40;
+
+  parse(dateString) {
+    return (0, _utils.parseAnyDigitsSigned)(dateString);
+  }
+
+  set(date, _flags, value) {
+    return [
+      (0, _index.constructFrom)(date, value * 1000),
+      { timestampIsSet: true },
+    ];
+  }
+
+  incompatibleTokens = "*";
+}
+exports.TimestampSecondsParser = TimestampSecondsParser;