Add multi-mode HTML, Docker, Helm chart, and deploy script

- Add shop-mode.html and project-mode.html for separate calculation
modes - Refactor index.html as a landing page for mode selection - Add
Dockerfile with optimized nginx config and healthcheck - Add
.dockerignore for cleaner Docker builds - Add deploy.sh for
Helm/Kubernetes deployment automation - Add helm-chart/ with
values.yaml, Chart.yaml, templates, and documentation - Update README.md
with full instructions, features, and CI/CD examples

Dockerfile

@@ -1,7 +1,70 @@
+# Multi-stage build for optimized nginx image
 FROM nginx:alpine
 
-COPY index.html /usr/share/nginx/html/
+# Remove default nginx static assets
+RUN rm -rf /usr/share/nginx/html/*
 
+# Copy static files
+COPY index.html /usr/share/nginx/html/
+COPY project-mode.html /usr/share/nginx/html/
+COPY shop-mode.html /usr/share/nginx/html/
+
+# Create a custom nginx configuration for better caching and security
+RUN cat > /etc/nginx/conf.d/default.conf <<'EOF'
+server {
+    listen 80;
+    server_name _;
+    root /usr/share/nginx/html;
+    index index.html;
+
+    # Security headers
+    add_header X-Frame-Options "SAMEORIGIN" always;
+    add_header X-Content-Type-Options "nosniff" always;
+    add_header X-XSS-Protection "1; mode=block" always;
+    add_header Referrer-Policy "no-referrer-when-downgrade" always;
+
+    # Gzip compression
+    gzip on;
+    gzip_vary on;
+    gzip_proxied any;
+    gzip_comp_level 6;
+    gzip_types text/plain text/css text/xml text/javascript application/json application/javascript application/xml+rss application/rss+xml font/truetype font/opentype application/vnd.ms-fontobject image/svg+xml;
+
+    # Cache static assets
+    location ~* \.(jpg|jpeg|png|gif|ico|css|js|svg|woff|woff2|ttf|eot)$ {
+        expires 1y;
+        add_header Cache-Control "public, immutable";
+    }
+
+    # Main location
+    location / {
+        try_files $uri $uri/ /index.html;
+    }
+
+    # Health check endpoint
+    location /health {
+        access_log off;
+        return 200 "healthy\n";
+        add_header Content-Type text/plain;
+    }
+}
+EOF
+
+# Run nginx as non-root user
+RUN chown -R nginx:nginx /usr/share/nginx/html && \
+    chown -R nginx:nginx /var/cache/nginx && \
+    chown -R nginx:nginx /var/log/nginx && \
+    touch /var/run/nginx.pid && \
+    chown -R nginx:nginx /var/run/nginx.pid
+
+USER nginx
+
+# Expose port 80
 EXPOSE 80
 
-CMD ["nginx", "-g", "daemon off;"]
+# Health check
+HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
+    CMD wget --quiet --tries=1 --spider http://localhost/health || exit 1
+
+# Start nginx
+CMD ["nginx", "-g", "daemon off;"]