- Add migration 0004 to introduce 'claiming' status and timeout index
- Add StatusClaiming to platformevent domain and allow it in Validate()
- Rewrite ListDue as transactional UPDATE ... RETURNING with FOR UPDATE SKIP LOCKED
- Add ReleaseStaleClaims to reset expired claiming events back to retrying
- Worker Start() now runs a 30s ticker for stale claim recovery (5m timeout)
- Update stubEventStore in tests to satisfy new EventStore interface
Refs: D-02
D-01: callback_target contract drift cleanup.
- Remove CallbackTarget from Event struct and Validate
- Remove CallbackTarget from PlatformInboundMeta
- Remove defaultCallbackTarget and assignment from builder
- Remove callback_target column from INSERT/SELECT/dead_letter SQL
- Clean up all test literals and assertions
DB migration left untouched; column remains empty until a future schema
cleanup migration.
