chore: add the Context7 ownership key

[myromartsin]

Summary

context7.json carries the ownership URL and public key issued by Context7 when the library was claimed, which links the repository to its Context7 entry for verification.

Motivation

Verified libraries rank higher in Context7 search.

Conformance impact

None.

Checklist

• Tests added or updated (or a rationale for why none)
• pnpm test, pnpm lint, pnpm format pass locally
• Docs reflect the change (per CONTRIBUTING.md)
• Commit message follows the project convention

[codspeed-hq]

Merging this PR will not alter performance

✅ 39 untouched benchmarks

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_{Comparing feat/context7-claim (a43acc8) with main (833ba88)}