Fix global error page, update CI workflow, add Dockerfile

Dockerfile

@@ -0,0 +1,42 @@
+# Use a multi‑stage build for a Next.js app
+
+# ---------- Builder stage ----------
+FROM node:20-alpine AS builder
+
+# Set working directory
+WORKDIR /app
+
+# Install dependencies (use package lock when present)
+COPY shop/package*.json ./
+RUN npm ci --omit=dev
+
+# Copy the source code
+COPY shop/ .
+
+# Build the production output
+RUN npm run build
+
+# ---------- Runtime stage ----------
+FROM node:20-alpine AS runner
+
+WORKDIR /app
+
+# Copy only the built assets and runtime dependencies from the builder
+COPY --from=builder /app/.next ./.next
+COPY --from=builder /app/public ./public
+COPY --from=builder /app/package*.json ./
+COPY --from=builder /app/next.config.mjs ./
+COPY --from=builder /app/next-env.d.ts ./
+COPY --from=builder /app/tsconfig.json ./
+
+# Install production dependencies (already installed in builder, but ensure they are present)
+RUN npm ci --omit=dev
+
+# Environment variables
+ENV NODE_ENV=production
+ENV PORT=3000
+
+EXPOSE 3000
+
+# Start the Next.js server
+CMD ["npm", "run", "start"]