Calibrate plan selection's costs from measured sketch costs #679

Plan selection prices candidates with analytical_cost (formulas). The measured-evidence cost and resource models, empirical_cost and empirical_resources (kept by #676, not wired in), are not used. Nothing calibrates plan selection from measured sketch costs, such as sketch-bench's per-operation costs (rqe_atomic_costs.json).

To do (after G4, which brings per-second cost and recurrence)

• Feed the measured per-operation costs from the deployment or study into plan selection's cost model.
• Fall back to analytical_cost where there is no measurement.
• Report which cost source priced each node.

Found in the #676 capability audit. Related: #660 (deployment cost models), #671.