to Support Safari Capture by SSR

[hon2be]

제안 커밋 메시지:

Summary

• Detect Safari in dom-to-image and fall back to a headless Puppeteer renderer so Safari users get a reliable capture instead of a blank image.
• Send the full SVG via multipart FormData from the browser; update the Express fallback server to accept the upload and render the SVG without truncation.
• Persist the generated HTML/PNG to temp/ for debugging, update the default port to 4000, and expose fallbackServer in the simplified test viewer.

Testing

• npm run start-server
• Open http://localhost:4000/examples/test-viewer.html in Safari
• Set fallbackServer to http://localhost:4000/render
• Capture several gradients/complex DOM nodes and confirm Safari now produces a non-cropped image

[hon2be]

@tsayen 검토, 병합 및 게시해 주시기 바랍니다.