docs: add CI, Codecov, npm, and license badges to README (fixes #49)

[hanu-14]

Adds CI, Codecov, npm version, and MIT license badges to the top of README.md.

[alphacrack]

Badges look correct and match #49. Two notes, neither blocking:

• The npm version badge will render as "package not found" until the first npm publish — expected, and fine to land now per the issue.
• This branch is stacked on #54, so the diff currently shows the examples change too; that resolves itself once #54 merges. No action needed.

[alphacrack]

Re-checked against the new main: MERGEABLE/CLEAN. Badge URLs are unaffected by today's toolchain changes. Merges after #54 (stacked). Ready.

[hanu-14]

Thanks for the review, alphacrack. The PR is clean and merges after #54. The badge URLs remain unaffected by the toolchain changes, so no updates are needed. Ready to merge.