Improve collision reaction section

Collision reaction is chaotic, messy and badly explained, it should be restructured.

Put more emphasis on shallow-axis reaction, followed by other, more specific stuff.

Find the collision reaction section in the repository's documentation, likely in a markdown or text file. Review the current structure and content. The goal is to reorganize it to emphasize shallow-axis reaction first, then other specific details. Check for any existing comments or linked resources to understand the intended improvements.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.