[P39.0] MASTER thin update Phase 38 complete / Phase 39 active

[DeliciousBuding]

Task

Thin docs/progress/MASTER.md for Phase 38 complete → Phase 39 active.

Facts

• Phase 38 closed via PRs docs(progress): MASTER Phase 37 complete / Phase 38 active (#798) #804–chore(shared): extract hubClient residual slice continue (#799) #808; tip ~5d0e151b
• Residual after P38: hubClient ~1323 · agent_dispatch ~924 · process_executor ~2122 · message/service ~805 · session/service ~793 · orchestrator ~818 · handlers ~772 · delivery_outbox ~425
• MASTER ≤150 lines; no product code

Allowed

• docs/progress/MASTER.md only