add docker build steps

web/dockerfile

@@ -0,0 +1,22 @@
+# Use an official Node runtime as a parent image
+FROM node:21-alpine
+
+# Set the working directory in the container to /app
+WORKDIR /app
+
+# Copy package.json and package-lock.json before other files
+# Utilise Docker cache to save re-installing dependencies if unchanged
+COPY package*.json ./
+
+# Install dependencies
+RUN npm install
+
+# Copy all files
+COPY . .
+
+# Build the app
+RUN npm run build
+
+# Serve the app on port 3000
+EXPOSE 3000
+CMD ["npm", "start"]