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/@tailwindcss/node/dist/esm-cache.loader.mjs

@@ -0,0 +1 @@
+import{isBuiltin as i}from"module";var o=async(a,e,u)=>{let r=await u(a,e);if(r.url===import.meta.url||i(r.url)||!e.parentURL)return r;let t=new URL(e.parentURL).searchParams.get("id");if(t===null)return r;let l=new URL(r.url);return l.searchParams.set("id",t),{...r,url:`${l}`}};export{o as resolve};