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/ISOTimezoneParser.js

@@ -0,0 +1,46 @@
+import { constructFrom } from "../../../constructFrom.js";
+import { getTimezoneOffsetInMilliseconds } from "../../../_lib/getTimezoneOffsetInMilliseconds.js";
+import { timezonePatterns } from "../constants.js";
+import { Parser } from "../Parser.js";
+
+import { parseTimezonePattern } from "../utils.js";
+
+// Timezone (ISO-8601)
+export class ISOTimezoneParser extends Parser {
+  priority = 10;
+
+  parse(dateString, token) {
+    switch (token) {
+      case "x":
+        return parseTimezonePattern(
+          timezonePatterns.basicOptionalMinutes,
+          dateString,
+        );
+      case "xx":
+        return parseTimezonePattern(timezonePatterns.basic, dateString);
+      case "xxxx":
+        return parseTimezonePattern(
+          timezonePatterns.basicOptionalSeconds,
+          dateString,
+        );
+      case "xxxxx":
+        return parseTimezonePattern(
+          timezonePatterns.extendedOptionalSeconds,
+          dateString,
+        );
+      case "xxx":
+      default:
+        return parseTimezonePattern(timezonePatterns.extended, dateString);
+    }
+  }
+
+  set(date, flags, value) {
+    if (flags.timestampIsSet) return date;
+    return constructFrom(
+      date,
+      date.getTime() - getTimezoneOffsetInMilliseconds(date) - value,
+    );
+  }
+
+  incompatibleTokens = ["t", "T", "X"];
+}