Replace broken images in README

Several images in the README are currently broken and no longer render correctly.

This appears to be related to the [public instance](https://github.com/anuraghazra/github-readme-stats/issues/3851) being shut down after the Vercel sponsorship ended. As a result, image URLs that depended on that instance are no longer valid.

**Proposed solution:**
* Update the README to use the new [GitHub Action–based](https://github.com/marketplace/actions/github-readme-stats-action) setup where applicable.
* Replace or remove broken image links.
* Ensure all images reference stable, long-term URLs.

**Alternative solution:**
* We could also use the new [whitelist](https://github.com/anuraghazra/github-readme-stats?tab=readme-ov-file#available-environment-variables) feature to deploy a limited vercel instance to generate the card.

**Expected outcome:**
The README renders correctly with no broken images and accurately reflects the current recommended usage of the project.