[v0.17 S2] Extract transport status behind ActivationService

[TheGreenCedar]

Package S2 in the v0.17.0 consolidated remediation program.

Contract

After every stdio point fix has landed, move transport status and activation
logic behind ActivationService. CLI code remains an adapter and cannot depend
directly on codestory_retrieval; add an executable architecture contract for
that direction.

Dependencies

W1.4, EV-5, EV-4, RUN-B, API, WIRE, and READY-B must land first in the declared
stdio_transport.rs order.

Program boundaries

• The implementation PR uses a codex/* branch, targets
  dev/codestory-next, and carries this issue as Closes #N.
• This is a behavior-preserving ownership move after the point fixes, not a
  second activation or retrieval system.
• Preserve packet as the broad-retrieval owner and CLI/HTTP/MCP as adapters.
• Do not touch product version surfaces or move mutable readiness authority out
  of runtime.

Done when

Transport status behavior and wire output are unchanged, the CLI has no direct
codestory_retrieval:: dependency, ActivationService owns the moved logic,
and architecture, stdio protocol, fidelity, and packet baselines pass without
movement.

Refs #1179