feat: Initial Docker Compose setup for conversation layer

Adds a docker-compose.yml to manage the OpenWA, Chat UI, and WhatsApp Router services.

Includes:
- Dockerfile and basic Node.js skeleton for Chat UI.
- Dockerfile and basic Node.js skeleton for WhatsApp Router.
- docker-compose.yml defining the three services, including:
    - Placeholder for OpenWA image (you must configure this).
    - Build contexts for UI and router.
    - Port mappings.
    - Environment variable examples.
    - Volume for OpenWA session persistence.
- Updated README.md with detailed setup, configuration, and usage instructions.

chat-ui/server.js

@@ -0,0 +1,11 @@
+const express = require('express');
+const app = express();
+const PORT = process.env.PORT || 3000;
+
+app.get('/', (req, res) => {
+  res.send('Chat UI is running!');
+});
+
+app.listen(PORT, () => {
+  console.log(`Chat UI listening on port ${PORT}`);
+});