DCRP-40: Rank-Two Planar Covariance and Normal-Compression Floquet Rigidity

Derives the exact evolution of the common vorticity-plane normal vector and the pseudo-determinant evolution of the in-plane covariance, proves that a purely kinematic global planar-vorticity Liouville theorem is false, and identifies the planar conformal Floquet mode as the true remaining branch.