Maity: Board

hub: MIN_POOL_PER_WORKER — remove it or give a reason that still holds

tsk-zm2z04ep2cma open

Follow-up of #1320 (tsk-4467sdqe3xt9, merged as e24ec17). MIN_POOL_PER_WORKER = 2 existed only for the shared count's second connection (#1276). Since #1320 the count has its own engine, so that reason is gone; the constant is marked "open" in code and KTW.

Do one of two, decided by measurement, not argument:

• remove the minimum, or
• keep it with a reason that holds now.

Measure the serving pool's use per worker (peak checked-out connections under the hub test load or a short local load on PostgreSQL), put the numbers in the PR, and update the KTW entry (open → active or superseded). Small hub PR; test on PostgreSQL before review.