Reduce the committed review receipt to a minimal attestation

[bigboateng]

Summary

• The artifact committed for a reviewed PR shrinks to a two-field attestation (reviewed_tree, program_fingerprint); the full sealed receipt (round trajectory, kernel receipt chain, final review bytes) is verified in full at seal time and archived only in the local review store.
• CI verification (review-verified) now performs three deterministic checks: strict attestation decode, program fingerprint recompiled from the base-revision admitted policy, and reviewed-tree recomputation from the PR head.
• The self-review yield skill is strictly report-only (verdict in conversation, no seal/commit/push); self-review-solve seals and commits the attestation locally but never pushes.

Verification

• Full repository contract suite (60 tests) plus go vet ./... and go test ./... pass locally.
• Both yield skill fixture tests pass; the branch self-review converged with the sealed attestation verifying against HEAD.