whaleflow: ARMH/RLM shared-memo integration with live engine + telemetry

[Hmbown]

Integrate the ARMH/RLM exact-context shared memo across workflow branches with the live engine, with visible hit/miss/cost telemetry per run.

Acceptance: two branches issuing identical context requests share one model call; memo hit/miss counts and saved cost appear in run telemetry.

Part of the v0.9.0 EPIC.