docs: fix broken star history badge (no token required)

[gautammanak1]

What was wrong

The star history section had two blocks. The first one, the star-history rank badge, does not work for this repository:

$ curl -sL -o /dev/null -w '%{http_code}\n' \
    'https://api.star-history.com/badge?repo=fetchai/innovation-lab-examples'
404
$ curl -sL 'https://api.star-history.com/badge?repo=fetchai/innovation-lab-examples'
not ranked

star-history only issues that badge for repositories in its ranking list, so the README was rendering a broken image.

What changed

Replaced the rank badge with shields.io badges that read live counts from the GitHub API — no token, no account, no login:

Badge	Source
Stars	img.shields.io/github/stars
Forks	img.shields.io/github/forks
Contributors	img.shields.io/github/contributors
Last commit	img.shields.io/github/last-commit

The star history chart is unchanged — api.star-history.com/svg returns 200 for both the light and dark variants, and needs no token either.

Verification

Every image URL in the README was checked; all 13 return 200. The 404 above was the only broken one.

Also considered starchart.cc as the chart source, but it was returning 400 rate limited on test, so the existing chart is the more reliable option.

[github-actions]

AI code review

This PR fixes a broken badge in the README by replacing the non-functional star-history rank badge with four shields.io badges that read live data from GitHub's public API. The change is purely documentation and all new URLs are verified to return 200.

How I read this change

• README.md: Replaced broken star-history rank badge (404 on api.star-history.com/badge) with four working shields.io badges for stars, forks, contributors, and last commit. The star history chart below remains unchanged.

No blocking issues found in this diff.

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This check passes. Findings are advisory.

_{Reviewed by ASI:One (asi1). Automated review is fallible — apply judgement.}