[P0][CORE-02] Durable state, outbox and artifacts

Parent: #1

## Objective
Make task/workspace state durable enough that crashes, restarts and external side effects never reduce the system to guessing from a chat transcript.

## Scope
- SQLite transactional state for workspaces, tasks, grants, operations and migrations.
- Event journal plus transactional outbox/inbox/consumer cursors.
- Unique operation IDs before externally significant dispatch.
- Content-addressed artifact store for evidence, patches, files, snapshots and protocol fixtures.
- Retention/GC that respects references, privacy scope and legal deletion.
- Atomic state + pending-dispatch persistence where required.

## Design requirements
- A worker must be able to resume from durable state without provider conversation history being authoritative.
- Side-effect intent is persisted before dispatch; observations/results are appended, not retroactively invented.
- Artifact hashes are immutable references; mutable metadata lives separately.

## Acceptance criteria
- [ ] Crash between state transition and dispatch leaves an unambiguous recoverable operation record.
- [ ] Crash after dispatch but before result recording produces an explicit uncertain/reconciliation state where appropriate.
- [ ] Database migrations are reversible/restore-tested for supported upgrade paths.
- [ ] Artifact integrity is checked by hash and corrupt/missing blobs fail visibly.
- [ ] Concurrent consumers cannot double-apply one journal event.
- [ ] Retention does not delete referenced evidence or leak deleted private derivatives.

## Tests
Crash/fault injection around every transaction boundary; duplicate-delivery tests; migration fixtures; disk-full/corruption simulations; artifact hash mismatch cases.

## Dependencies
- CORE-01

**First phase:** P0
**Maturity target:** P1
**Workstream:** Runtime and contracts

Start with the CORE-01 dependency and the stated scope for SQLite state, the event journal, transactional outbox/inbox, and the artifact store. Run the listed crash and fault-injection tests, duplicate-delivery tests, migration fixtures, disk-full and corruption simulations, and hash-mismatch cases. Done means the acceptance criteria hold across recovery, migrations, concurrency, retention, and artifact integrity.

Written by the indexing model from the issue text.