feat(delivery): implement delivery scheduler and state machine
Core delivery service with: task creation (idempotent, validated),
background scheduler (claimAndReserve with SELECT FOR UPDATE SKIP
LOCKED), 4-level concurrency control, resource quota enforcement,
host allocation from candidate pool, AWX job dispatch, polling,
TCP health check, instance registration, CloudDM integration
(optional), and cancel support. 11-state machine with optimistic
locking and full event audit trail.
Relates-to: #97
mac
e11bc6f3d6