feat: Dockerfile and docker-compose

Dockerfile: node:20-alpine, exposes 3456, STORE_PATH=/app/data/store.json.
docker-compose.yml: proxy service with ./data volume mount + inline comments
showing how to wire GOCARDLESS_BASE_URL into an existing actual-server compose.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,20 @@
+FROM node:20-alpine
+
+WORKDIR /app
+
+# Install dependencies first (layer cache)
+COPY package.json ./
+RUN npm install --omit=dev
+
+# Copy source
+COPY src/ ./src/
+
+# Data directory (override with a volume)
+RUN mkdir -p /app/data
+
+EXPOSE 3456
+
+ENV NODE_ENV=production
+ENV STORE_PATH=/app/data/store.json
+
+CMD ["node", "src/server.js"]

docker-compose.yml

@@ -0,0 +1,51 @@
+# docker-compose.yml
+#
+# Standalone: run just the proxy
+#   docker compose up
+#
+# With actual-server: paste the `gocardless-proxy` service block into your
+# existing actual-server compose file and add GOCARDLESS_BASE_URL to actual-server.
+#
+# Run one-time setup BEFORE starting the proxy:
+#   docker compose run --rm gocardless-proxy node src/setup.js
+
+services:
+  gocardless-proxy:
+    build: .
+    # or use a pre-built image:
+    # image: ghcr.io/yourname/actual-gocardless-proxy:latest
+    container_name: gocardless-proxy
+    restart: unless-stopped
+    ports:
+      - "3456:3456"
+    volumes:
+      # Persist credentials, tokens, requisitions, and account mappings across restarts
+      - ./data:/app/data
+    environment:
+      PORT: 3456
+      STORE_PATH: /app/data/store.json
+      # Set PROXY_BASE_URL to the URL that Enable Banking will redirect to after OAuth.
+      # Must be reachable by the user's browser.
+      # Examples:
+      #   http://localhost:3456          (local dev, browser on same machine)
+      #   https://yourserver.example.com (reverse-proxied, production)
+      # This can also be set during `npm run setup`.
+      # PROXY_BASE_URL: http://localhost:3456
+
+# ─────────────────────────────────────────────────────────────────────────────
+# How to wire this into your existing actual-server compose file:
+# ─────────────────────────────────────────────────────────────────────────────
+#
+# 1. Add the gocardless-proxy service above to your docker-compose.yml
+# 2. Add GOCARDLESS_BASE_URL to actual-server's environment:
+#
+#   actual-server:
+#     image: actualbudget/actual-server:latest
+#     environment:
+#       GOCARDLESS_BASE_URL: http://gocardless-proxy:3456
+#       # ... your other env vars
+#     depends_on:
+#       - gocardless-proxy
+#
+# 3. Make sure both services are on the same Docker network (they will be
+#    automatically if they're in the same compose file).