Enhance portfolio images for the web

Smaller file size, better loading time and browsing experience (especially for mobile visitors). :)

Could you also please add the hacktoberfest label to this issue?

Thank you! :)

Please feel free to ask me if you'd like more issues to be fixed!

Start by locating the portfolio image assets and checking their current file sizes and loading behavior, especially on mobile. Done means the images use smaller files while preserving an improved browsing experience and faster loading; the issue also requests the hacktoberfest label.

Written by the indexing model from the issue text.