Consolidate V0 embodiment and recovery contracts

[nicoechaniz]

Issue

Closes #42
Closes #27

Claim-ID: a14685f8-3f09-4749-8e5f-4985a91452be
Deployment: not deployed

Outcome

Consolidates the reviewed pre-release V0 embodiment, recovery, collective-memory, harness, authority-epoch, and two-host contracts into one exact candidate. It also fixes coordination receipt semantics so rejected commands cannot mutate the effective PR linkage, accepted reclaims clear historical PRs, and accepted review binds the current PR.

Exact candidate

• Head: 306900c
• Tree: be24a07fd387c9fe10331b17507904f14f66ea71
• Cluster consumer pin: 306900c

Invariants

• Identity and provenance remain verifiable.
• No private memory or credentials were added.
• Pre-release contracts fail closed; obsolete compatibility paths are not retained.
• Rejected coordination commands preserve the authoritative PR/claim/scope/branch state.

Tests

• Full Matrix suite: 597 tests OK, 19 optional-contract skips, exit 0.
• Coordination/CLI suite: 45 passed, including hostile rejected claim/review/heartbeat/release cases and reclaim after expiry/release.
• Cluster consumer suite against this exact pin: 478 passed, 4 skipped.
• Disposable restic export E2E: 1 passed.
• Disposable recovery-rebirth E2E: 1 passed.
• Exact-head adversarial review: GREEN.
• git diff --check: clean.

Security and rollback

No deployment, SSH, host, custody, or production mutation is included. Roll back by reverting the merge commit; persistent/live migration is deferred to separately authorized gates.