Add Dokploy-specific Dockerfile and update docs

Dockerfile.dokploy

@@ -0,0 +1,29 @@
+# Production-ready Dockerfile for Dokploy deployments
+# Use a Debian-based Node image to ensure native modules such as bcrypt have prebuilt binaries available.
+FROM node:20-slim AS base
+
+# Create application directory inside the container
+WORKDIR /app/backend
+
+# Set production environment variables inside the image.
+ENV NODE_ENV=production \
+    PORT=3000
+
+# Install only the production dependencies defined in the backend package.json.
+COPY backend/package*.json ./
+RUN npm ci --omit=dev \
+    && npm cache clean --force
+
+# Copy backend source code and the static frontend bundle into the container.
+COPY backend/src ./src
+COPY frontend ../frontend
+
+# Use the non-root "node" user that is precreated in the base image.
+RUN chown -R node:node /app
+USER node
+
+# Expose the HTTP port used by the Express server.
+EXPOSE 3000
+
+# Start the Express API / Socket.IO server.
+CMD ["node", "src/server.js"]