Adds an env2-owned HTTP sink container (scadabridge-env2-sfsink) whose 503
mode makes ExternalSystem.CachedCall buffer, and an EnvSoak template whose 2 s
SoakTick sends one tick-numbered cached call, so loss and duplicates are
countable at the sink.
Claude-Session: https://claude.ai/code/session_01GT67ACmpMR7b9LGRPLijMi
Joseph Doherty