feat(runtime-v2): Wave 1 — entity persistence, events, API, CLI for Lease/Execution/Checkpoint + idempotency + reconcile sessions

Wire three domain entities end-to-end following the Sandbox pattern:
- Lease: SQLite table, 5 CRUD methods, 5 events, 5 API endpoints, CLI subcommand
- Execution: SQLite table, 5 CRUD methods, 5 events, 4 API endpoints, CLI subcommand
- Checkpoint: SQLite table, 6 CRUD methods, 5 events, 5 API endpoints, CLI subcommand

Cross-cutting infrastructure:
- Idempotency key framework: idempotency_keys table, check/save helpers,
  applied to create_sandbox and terminate_sandbox handlers
- Reconcile session metadata: reconcile_sessions table, action identity
  hashing, orchestrator integration for deterministic resume
- Health poller: restore_from_store() for rehydrating after restart

Beads closed: vz-c0z, vz-k3l, vz-22d, vz-3hx, vz-v2n.1.3

626 tests passing (447 vz-stack + 13 vz-api + 166 vz-cli)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: lightsofapollo