fix: add nginx config for SPA routing in production

- Create nginx.conf with try_files directive for React Router
- Update Dockerfile.prod to copy nginx configuration
- Fixes 404 errors on direct navigation to /login, /register, etc.
- Add gzip compression and static asset caching

frontend/Dockerfile.prod

@@ -26,8 +26,8 @@ FROM nginx:alpine
 # Copy built assets from builder stage
 COPY --from=builder /app/dist /usr/share/nginx/html
 
-# Copy nginx configuration (if needed)
-# COPY nginx.conf /etc/nginx/conf.d/default.conf
+# Copy nginx configuration for SPA routing
+COPY nginx.conf /etc/nginx/conf.d/default.conf
 
 # Expose port
 EXPOSE 80