Resolve "README.md: Header image scale not limited"

What does this MR do?

Fixes the max-width with 100$ for loaded images in the wiki, preview + activity stream.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Review
  • Has been reviewed by Frontend

What are the relevant issue numbers?

Closes #37058 (closed),#37024 (closed),#37230 (closed)