fix(security): enhance security headers and tighten CORS configuration

- Configure custom Content Security Policy for React app compatibility
- Add Permissions-Policy header to disable unnecessary browser features
- Set HSTS to 1 year with preload flag for better transport security
- Update referrer policy to strict-origin-when-cross-origin
- Restrict CORS localhost origins to development environment only
- Production deployments now only allow configured FRONTEND_URL and ADMIN_URL
- Addresses security headers configuration issues from security scan

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/server.js

@@ -28,20 +28,54 @@ const adminAuthRoutes = require('./src/routes/adminAuth');
 const app = express();
 const PORT = process.env.PORT || 3000;
 
-// Security middleware
-app.use(helmet());
+// Security middleware with custom CSP
+app.use(helmet({
+  contentSecurityPolicy: {
+    directives: {
+      defaultSrc: ["'self'"],
+      scriptSrc: ["'self'", "'unsafe-inline'"], // Required for React
+      styleSrc: ["'self'", "'unsafe-inline'", "https:"], // Required for styled components
+      imgSrc: ["'self'", "data:", "https:", "blob:"], // Allow data URLs and external images
+      connectSrc: ["'self'"], // API connections
+      fontSrc: ["'self'", "https:", "data:"], // Web fonts
+      objectSrc: ["'none'"], // Disable plugins
+      mediaSrc: ["'self'"], // Audio/video
+      frameSrc: ["'none'"], // Disable iframes
+    },
+  },
+  hsts: {
+    maxAge: 31536000, // 1 year
+    includeSubDomains: true,
+    preload: true
+  },
+  permittedCrossDomainPolicies: false,
+  referrerPolicy: { policy: "strict-origin-when-cross-origin" }
+}));
+
+// Additional security headers
+app.use((req, res, next) => {
+  // Permissions Policy (controls browser features)
+  res.setHeader('Permissions-Policy', 'camera=(), microphone=(), geolocation=(), payment=()');
+  next();
+});
 
 // CORS configuration
 const corsOptions = {
   origin: function (origin, callback) {
     const allowedOrigins = [
       process.env.FRONTEND_URL || 'http://localhost:3005',
-      process.env.ADMIN_URL || 'http://localhost:3005',
+      process.env.ADMIN_URL || 'http://localhost:3005'
+    ];
+    
+    // In development, also allow localhost origins
+    if (process.env.NODE_ENV === 'development') {
+      allowedOrigins.push(
         'http://localhost:5173', // Vite dev server
         'http://localhost:3002', // Backend server
         'http://localhost:3001', // For API testing
         'http://localhost:3000'  // Direct backend access
-    ];
+      );
+    }
     
     // Allow requests with no origin (like mobile apps or curl)
     if (!origin || allowedOrigins.indexOf(origin) !== -1) {