[Visual]: Optimize README banner image resolution for mobile & high-DPI screens

[githubmofo]

🐛 What is the bug?

The TorusGuard.png banner in README.md is currently embedded with <img width="300">. On high-DPI retina screens and mobile GitHub apps, the image can appear slightly scaled or display with high dark contrast on pure white themes.

🎯 Expected Behavior

The banner should be crisp on all display scales and look seamless across both GitHub Dark Mode and Light Mode.

💡 Suggested Fix

1. Add an @2x optimized asset or responsive <picture> tag.
2. Ensure consistent padding and mobile responsiveness in README.md.