Remove PNG server generation functionality

- Remove PNG server generation option from DownloadButton component
- Remove PNG generation logic from download route
- Delete pngGenerator.cjs and related test files
- Simplify download options to focus on frontend PNG export
- Reduce server complexity and resource usage

package.json

@@ -57,8 +57,10 @@
     "embla-carousel-react": "^8.5.2",
     "express": "^4.18.2",
     "helmet": "^7.1.0",
+    "html2canvas": "^1.4.1",
     "input-otp": "^1.4.2",
     "jsonwebtoken": "^9.0.2",
+    "jspdf": "^3.0.1",
     "lucide-react": "^0.364.0",
     "next-themes": "^0.4.4",
     "nodemon": "^3.0.2",