M11-T03: Implement deterministic hold lifecycle with dedupe and replay equivalence

[skel84]

Summary

Implement the core reservation-core lifecycle and prove that live apply and replay produce the same results.

Scope

• CreatePool
• PlaceHold
• ConfirmHold
• ReleaseHold
• operation dedupe and conflict detection
• snapshot/WAL replay through the same apply path

Acceptance

• duplicate retry returns cached result
• conflicting operation_id reuse returns conflict
• deterministic invalid-state rejection
• replay equivalence holds across crash/restart boundaries

Canonical docs

• docs/reservation-engine-plan.md
• docs/reservation-semantics.md

Blocked by

• M11 umbrella issue
• M11-T02