feat: add OpenTimestamps temporal-anchor profile

[safal207]

What changed

Adds an experimental Bitcoin OpenTimestamps sidecar profile for independently bounding when exact decision bytes existed:

• a live adapter that invokes the official ots verify client against exact temporary copies of the target and proof;
• fail-closed result states: TEMPORALLY_ANCHORED, PENDING, INVALID, and UNAVAILABLE;
• eight deterministic conformance vectors for verified, pending, nonzero-exit, unknown, missing, duplicate, and conflicting attestation outputs;
• a bounded integration shape for GuardrailDecision temporal-anchor sidecars;
• a read-only CI gate for the deterministic parser contract.

Why

issued_at inside a hashed record is tamper-evident after issuance but does not prevent the issuer from choosing a favorable timestamp before hashing. A verified OpenTimestamps proof can establish that the exact subject bytes existed no later than an attested Bitcoin block.

The profile deliberately does not promote a URL, claimed block height, proof filename, exit code, or success-looking string by itself. It also keeps pending calendar proofs pending rather than treating them as anchored.

Validation

PASS verified-bitcoin-attestation -> TEMPORALLY_ANCHORED/BITCOIN_ATTESTATION_VERIFIED
PASS pending-calendar-proof-stays-pending -> PENDING/BITCOIN_CONFIRMATION_PENDING
PASS success-looking-output-with-nonzero-exit-fails-closed -> INVALID/VERIFIER_EXIT_NONZERO
PASS zero-exit-without-bitcoin-attestation-fails-closed -> INVALID/NO_BITCOIN_ATTESTATION
PASS unknown-attestation-is-not-bitcoin-proof -> INVALID/UNKNOWN_ATTESTATION
PASS conflicting-block-attestations-fail-closed -> INVALID/CONFLICTING_BITCOIN_ATTESTATIONS
PASS duplicate-attestations-are-ambiguous -> INVALID/AMBIGUOUS_MULTIPLE_ATTESTATIONS
PASS pending-and-confirmed-output-is-conflicting -> INVALID/CONFLICTING_PENDING_AND_CONFIRMED

OTS temporal-anchor conformance passed: 8

Run with:

python3 scripts/check_ots_anchor_vectors.py \
  conformance/guardrail-decision-v1/ots/manifest.json

Scope boundary

This PR does not reimplement OpenTimestamps cryptography, run a Bitcoin node in CI, stamp production decisions, or claim authorship/correctness/freshness from a temporal proof. Live cryptographic verification remains delegated to the official OpenTimestamps client and its Bitcoin data source.

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• Commit unit tests in branch agent/ots-temporal-anchor-profile

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