Extract ImageService + ResourceService + StatsService; Agent becomes thin coordinator

[HyeockJinKim]

Extract image handling, resource acquire/release (alloc_map allocate/free, PortPool allocate/free), and stat collection into services. Resource managers use the existing symmetric primitives (no new common interface). Agent becomes a thin coordinator over these + KernelService/LifecycleService. Priority target = Sokovan-driven ops (check_and_pull -> ImageService, assign_port -> ResourceService); commit/push/purge, scan_gpu_alloc_map etc. deferred.

Success Criteria:

• image/resource/stats flows route through their services with parity (via the Prepare open-source release #1 CLI).
• alloc_map + PortPool acquire/release owned by ResourceService (symmetric, idempotent release).
• AbstractAgent field/method count materially reduced (thin coordinator).
• pants test passes for affected packages

JIRA Issue: BA-6763