feat: add initial Socket.IO queue server implementation

- Created a basic Socket.IO server that manages user connections and queues for events.
- Implemented queue logic to handle concurrent user limits and JWT token issuance.
- Added MySQL configuration for potential persistence of queue positions.
- Introduced environment variables for configuration through a .env.example file.

README.md

@@ -34,3 +34,55 @@ You can check out [the Next.js GitHub repository](https://github.com/vercel/next
 The easiest way to deploy your Next.js app is to use the [Vercel Platform](https://vercel.com/new?utm_medium=default-template&filter=next.js&utm_source=create-next-app&utm_campaign=create-next-app-readme) from the creators of Next.js.
 
 Check out our [Next.js deployment documentation](https://nextjs.org/docs/app/building-your-application/deploying) for more details.
+
+## Queue / Ticketing demo (WebSocket + JWT)
+
+This repository contains a minimal demo of a queue system for high-concurrency ticket sales. Key ideas:
+
+- When an event reaches a concurrency threshold (e.g. 100 users), the server enables a queue for that event.
+- Users connect via WebSocket (Socket.IO). When queueing is active they are placed in a FIFO queue.
+- The server grants access (issues a signed JWT) to up to CONCURRENT_ACTIVE users (default 50) at a time.
+- The JWT is valid for a short period (default 15 minutes). When it expires the server revokes access and grants the next users in queue.
+- The client uses the JWT to authenticate purchase API calls.
+
+Files added in this demo:
+
+- `server/index.js` — simple Socket.IO server with in-memory queue logic and JWT issuance (demo only).
+- `.env.example` — example environment variables for running the socket server.
+- `app/page.tsx` — client UI (Next.js) that connects via Socket.IO and displays queue position, estimated wait, and purchase button.
+
+Important notes and limitations:
+
+- The server implementation in `server/index.js` is an in-memory demo. For production use a shared, persistent store (Redis) for queue/locks and a robust MySQL schema if you need persistence.
+- Add authentication, rate-limiting, and persistent sessions before using in production.
+
+Running locally
+
+1. Copy `.env.example` to `.env` and adjust values (especially `JWT_SECRET`).
+2. Install dependencies for the server and client:
+
+```powershell
+pnpm install
+pnpm --filter . add socket.io socket.io-client jsonwebtoken dotenv mysql2
+```
+
+3. Start the Socket.IO server:
+
+```powershell
+node server/index.js
+```
+
+4. Start the Next.js dev server:
+
+```powershell
+pnpm dev
+```
+
+5. Open `http://localhost:3000` and the client will connect to the socket server (default `http://localhost:4000`).
+
+Next steps / improvements
+
+- Move queue state to Redis (ZSET) to support multiple server instances.
+- Persist issued tokens and sessions in DB to support revocation and auditing.
+- Add server-side validation of the JWT on purchase endpoints.
+- Add tests around queue promotion logic and token expiration.