fix: repair dead documentation links

[tomatotomata]

Summary

Fixes #13404 by repairing the stale external documentation links reported by the repository's Check Markdown links workflow:

• replace npm package pages that returned checker-blocked 403 responses with the maintained GitHub repositories
• update the Aztec contract examples link from the removed master/noir-projects/noir-contracts/contracts path to the current next/docs/examples/contracts path
• point the vlayer reference at the current blog index after the old article URL began returning 404

The change is limited to the three docs references identified by the linked workflow run.

Validation

• npx --yes markdown-link-check docs/docs/guides/how_to_use_oracles.md --config docs/link-check.config.json -q
• npx --yes markdown-link-check docs/docs/guides/thinking_in_circuits.md --config docs/link-check.config.json -q
• npx --yes markdown-link-check docs/docs/project_structure/crates_and_packages.md --config docs/link-check.config.json -q
• git diff --check

The focused link checks pass on commit d310b52. The repository contribution guide asks for the documentation label; the fork token cannot add repository labels, so the changed paths and PR scope make the required category explicit for the maintainer.

Let me know what you think.

[github-actions]

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