docs: define 0.9 calibration planner

Defines the reviewed experiment-design contract for calibration planning.

Documents sensitivity-weighted I-optimal design, prospective covariance,
operating priorities, repeats, feasibility, conditioning, diminishing
returns, deterministic quadrature, full-range uncertainty, and exhaustive
finite search.

Records the numerical validation and benchmark gates that must be satisfied
during implementation and adds the supporting optimal-design references.

Author: GregRR