docs: Add test coverage badge to README (#500)

[Bhagyashri77777]

Hi @imDarshanGK,
I have added the Codecov badge to the README.md as requested in issue #500. This will track the test coverage once fully integrated into the CI pipeline.
Let me know if you need any changes!
Fixes #500

[Bhagyashri77777]

Hi @imDarshanGK!

Just wanted to give a quick update: I have successfully submitted the Pull Request (#867) to add the Codecov test coverage badge!

Looking forward to your review. Please let me know if any further changes are needed. Thank you!

[imDarshanGK]

@Bhagyashri77777 not working and add demo

[Bhagyashri77777]

Hi @imDarshanGK, thanks for the review!

Regarding the requested changes:

1. Demo: I will take a screenshot of the live site, add it to the assets/ folder as preview.png, and uncomment the Preview section in the README.md.
2. Coverage Badge: The Codecov badge currently shows as "not working/unknown" because the ci.yml workflow runs standard pytest but isn't generating or uploading coverage reports yet (e.g., using pytest-cov).

Would you like me to add the coverage generation steps to the GitHub Actions CI as part of this PR so the badge activates? Or do you have a different coverage tool in mind? Let me know and I will update it immediately!

[Bhagyashri77777]

Hi @imDarshanGK, I have pushed the requested updates!

1. Added the clean, full-screen demo screenshot (preview.png) and uncommented the Preview section in the README.
2. The Codecov badge is also added and ready to track coverage once the CI pipeline starts uploading reports.

Let me know if it looks good to merge!