docs: update graphics

[m1ghtym0]

• Add concept design to readme and intro
• Update components with black instead of purple on green
• Backport both to 0.7

[github-actions[bot]]

PR Preview Action v1.4.7 :---: Preview removed because the pull request was closed. 2024-06-18 07:19 UTC

[katexochen]

There is also https://github.com/edgelesssys/contrast/blob/main/docs/docs/_media/personas.svg with the purple on green.