Add Dockerfile and .dockerignore for Portainer build

.dockerignore

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+node_modules
+npm-debug.log
+Dockerfile
+.dockerignore
+.next
+

Dockerfile

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+# Use official Node.js image
+FROM node:20
+
+# Create app directory
+WORKDIR /app
+
+# Copy dependency files
+COPY package*.json ./
+
+# Install dependencies
+RUN npm install
+
+# Copy rest of the app
+COPY . .
+
+# Build the Next.js app
+RUN npm run build
+
+# Expose default Next.js port
+EXPOSE 3000
+
+# Start the server
+CMD ["npm", "start"]
+