InstantAdPay site skeleton: SIWE auth, live chain ledger, join links, buy flow

Zero-dependency Node server on the RM Circle pattern. Chain config lives in
the volume so the same code runs the Amoy dress rehearsal and mainnet.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docker-compose.yml

@@ -0,0 +1,15 @@
+services:
+  instantadpay:
+    build: .
+    restart: unless-stopped
+    environment:
+      NODE_ENV: production
+      PORT: 3000
+      ADMIN_PASSWORD: ${ADMIN_PASSWORD}
+      DATA_DIR: /app/data
+    volumes:
+      - instantadpay-data:/app/data
+    ports:
+      - "3000:3000"
+volumes:
+  instantadpay-data: