Add Docker image, example compose file and Gitea build workflow

- Dockerfile: node:24-alpine, production deps only, runs as the node
  user, healthcheck on /healthz. No volume, because the server keeps
  no state.
- docker-compose.yml: example for the VPS. It publishes no ports,
  since Docker's port publishing bypasses ufw and would skip NPM's IP
  access list. It joins NPM's network instead.
- .gitea/workflows/docker.yml: on v*-prod* tags, builds on the
  self-hosted runner and pushes v0idf1sh/sdp-dashboard:<tag> and
  :latest using the DHUB_UNAME and DHUB_PASS secrets.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.dockerignore

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+.git
+.gitea
+.vscode
+node_modules
+npm-debug.log*
+.env
+.env.*
+docs
+images
+*.md
+Dockerfile
+docker-compose*.yml

.gitea/workflows/docker.yml

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+# Builds the image and pushes it to Docker Hub when a production tag (e.g. v1.1.0-prod1) is pushed.
+# Restarting the container on the VPS is done by hand for now.
+name: Build and push image
+
+on:
+  push:
+    tags:
+      - 'v*-prod*'
+
+env:
+  IMAGE: v0idf1sh/sdp-dashboard
+
+jobs:
+  build:
+    runs-on: self-hosted
+    steps:
+      - name: Check out
+        uses: actions/checkout@v4
+
+      - name: Log in to Docker Hub
+        env:
+          DHUB_UNAME: ${{ secrets.DHUB_UNAME }}
+          DHUB_PASS: ${{ secrets.DHUB_PASS }}
+        run: echo "$DHUB_PASS" | docker login --username "$DHUB_UNAME" --password-stdin
+
+      - name: Build
+        run: |
+          docker build \
+            --pull \
+            --label "org.opencontainers.image.version=${{ gitea.ref_name }}" \
+            --label "org.opencontainers.image.revision=${{ gitea.sha }}" \
+            -t "$IMAGE:${{ gitea.ref_name }}" \
+            -t "$IMAGE:latest" \
+            .
+
+      - name: Push
+        run: |
+          docker push "$IMAGE:${{ gitea.ref_name }}"
+          docker push "$IMAGE:latest"
+
+      - name: Log out
+        if: always()
+        run: docker logout

Dockerfile

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+FROM node:24-alpine
+
+WORKDIR /app
+ENV NODE_ENV=production
+
+# install dependencies first so code-only changes reuse this layer
+COPY package.json package-lock.json ./
+RUN npm ci --omit=dev && npm cache clean --force
+
+COPY src ./src
+
+# no volume: sessions live in each user's browser, so the container keeps no state
+USER node
+EXPOSE 3000
+
+HEALTHCHECK --interval=30s --timeout=5s --start-period=10s --retries=3 \
+    CMD wget -qO- http://127.0.0.1:3000/healthz || exit 1
+
+CMD ["node", "src/server.js"]

docker-compose.yml

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+# Example compose file for the VPS. Copy src/env.example to .env next to this file and fill it in.
+# Nginx Proxy Manager forwards the subdomain to sdp-dashboard:3000 and enforces the IP allow list.
+
+services:
+  sdp-dashboard:
+    image: v0idf1sh/sdp-dashboard:latest
+    container_name: sdp-dashboard
+    restart: unless-stopped
+    env_file: .env
+    environment:
+      # must match the redirect URI registered in the Zoho API console, minus /auth/callback
+      PUBLIC_URL: https://dashboard.example.com
+    # No published ports on purpose. Docker's port publishing bypasses ufw, so "3000:3000" would
+    # let anyone reach the app directly and skip NPM's access list. NPM reaches it over the
+    # shared network instead, using the container name as the forward hostname.
+    expose:
+      - "3000"
+    networks:
+      - proxy
+
+networks:
+  proxy:
+    # the network Nginx Proxy Manager's container is on; check with `docker network ls`
+    external: true
+    name: ${NPM_NETWORK:-npm_default}