modules: re-point twap-monitor onto pool submit/status via the cow adapter

[mfw78]

Part of #138. Wave I — the second half of twap's 'migrated once': the chassis port landed on the legacy CowApiHost seam (#147/PR #240); this re-points it onto the pool.

Scope. Re-point modules/twap-monitor/src/strategy.rs from the legacy CowApiHost/shepherd:cow world onto pool submit + status through the cow adapter (venue-id), dropping the direct shepherd:cow/cow-api import and the shepherd-sdk cow client dependency.

Blocked by: the bundled cow adapter (G3), MockVenue (#149).

Acceptance. twap submits + tracks CoW orders through the pool; MockHost/MockVenue tests pass as behaviour-identity proof; no residual shepherd:cow import.