MySQL data layer: accounts, sessions, campaigns, burns (Marty: real concurrency)

Coolify MySQL (instantadpay-db) via DATABASE_URL; db.js bootstraps schema
and one-time imports the volume JSON. accounts/auth/ads are dual-mode: the
MySQL path uses guarded UPDATEs for the concurrent ad-serving hot path;
without DATABASE_URL the JSON stores remain (local dev). All data functions
async; server boots through db.init. Chain index stays a file: it is a
rebuildable cache of the blockchain, which remains the money truth.

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

Dockerfile

@@ -1,5 +1,7 @@
 FROM node:22-alpine
 WORKDIR /app
+COPY package.json ./
+RUN npm install --omit=dev --no-audit --no-fund
 COPY . .
 RUN mkdir -p /app/data
 ENV NODE_ENV=production