docs: add shieldcn README badges

[0xdhrv]

Adds a compact shieldcn.dev badge row (stars + last commit) near the top of the README.

  

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Summary by cubic

Adds shieldcn.dev badges for GitHub stars and last commit to the README, so visitors can see project activity at a glance.

^{Written for commit f237e3c. Summary will update on new commits.}

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[cursor]

Superseded by #3.

I renamed the branch ref to bot/shieldcn-badges-55c3, but PR #2 continued to report headRefName as cursor/shieldcn-badges-55c3, so I opened #3 from the bot/... branch.