Snapshot signed quorum inputs before asynchronous checks

[aruintelligence]

Change

• Snapshot ordinary JSON before asynchronous signed-report verification, signing, quorum creation, public-key fingerprinting, and held-input replay.
• Bind verdicts and input fingerprints to those call-time bytes even if a caller mutates its live objects while Web Crypto yields.
• Keep a non-JSON witness input rejected after entry, even if a caller removes the invalid field during replay.

Verification

• 905 Node tests passed locally, including mutation-during-signing, quorum counting, held-policy, witness, public-key fingerprint, and invalid-input regression checks.
• Project-authored Python/JavaScript signed-quorum comparison passed locally.
• Proof replay, API stability, upgrade contract, installed-package consumer compatibility, CLI contract, package artifact, local links, proof/verifier surfaces and claims, contract snapshot/drift, and git diff --check passed locally.
• GitHub CI is pending for this PR.

Scope and limits

No saved JSON schema or threshold semantics change. valid, threshold_met, policy_met, and witness_met remain separate. The snapshot only addresses mutation of live JavaScript inputs after a call begins; it does not authenticate the source of supplied files, signer identities, independence, or a trusted clock. The Python verifier is project-authored, not independent certification.