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>

Dockerfile

@@ -0,0 +1,8 @@
+FROM node:22-alpine
+WORKDIR /app
+COPY . .
+RUN mkdir -p /app/data
+ENV NODE_ENV=production
+ENV PORT=3000
+EXPOSE 3000
+CMD ["node","server.js"]