fix: restore Hardhat CI OpenZeppelin dependency

[moonrager13]

Fixes the failing Hardhat test workflow identified from Actions logs.

• Adds the missing exact @openzeppelin/contracts 5.6.1 dependency required by contracts/AgentExecutorAccess.sol.
• Updates the artifact workflow to use npm install, so the newly declared dependency is installed even though the existing lockfile predates it.
• No deployment or blockchain execution changes.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Regenerate the lockfile with the new dependency

Adding @openzeppelin/contracts here without updating package-lock.json leaves the committed lockfile out of sync: the lockfile root dependencies still omit this package and there is no node_modules/@openzeppelin/contracts entry. I checked the remaining workflows, and .github/workflows/ci.yml, validate.yml, build-check.yml, release.yaml, and others still run npm ci; the npm-ci(1) docs state that if package-lock dependencies do not match package.json, npm ci exits instead of updating the lock. Those CI jobs will fail before compiling/tests until the lockfile is regenerated or the workflows are changed consistently.

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