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/json5/lib/parse.d.ts

@@ -0,0 +1,15 @@
+/**
+ * Parses a JSON5 string, constructing the JavaScript value or object described
+ * by the string.
+ * @template T The type of the return value.
+ * @param text The string to parse as JSON5.
+ * @param reviver A function that prescribes how the value originally produced
+ * by parsing is transformed before being returned.
+ * @returns The JavaScript value converted from the JSON5 string.
+ */
+declare function parse<T = any>(
+    text: string,
+    reviver?: ((this: any, key: string, value: any) => any) | null,
+): T
+
+export = parse