Improve Lightbox: Escape key support & Image size optimization

[zihanKuang]

Description
This PR introduces two improvements to the documentation:

1. Lightbox Enhancement: Adds support for closing the modal when the Escape key is pressed.
2. Image Display Optimization: Ensures that both Markdown images and <img> elements are properly scaled to avoid overly large displays by default.

This improves user experience by preventing images from taking up excessive space and making the Lightbox more user-friendly.

Notes for Reviewers

• My local environment displays images correctly, but the official site shows different images, even though the paths are identical.
• Could this be a CDN caching issue, or is there another caching layer affecting images?
• Does the site apply any automatic image processing that might alter them?

Any insights would be greatly appreciated. Thank you! 😊

• Yes, I signed my commits.

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