X72-66: Fixed-Size Jost-Riccati Graph Anchor

Continuing from the dense approximate-inverse-matrix storage bottleneck identified in Round 65 (STOP-C69), this round writes the six-dimensional transfer state in 3+3 block form, representing the positive-viscosity minimal three-dimensional bundle as the Möbius pullback of a fixed-size 3×3 Riccati graph G_n, and proves the "Central Riccati Readout Theorem" a₃(ν)=-(G₁)₂₂, reducing certificate memory to O(1) and time to just O(J). Using this framework, it obtains a new rigorous microscopic anchor point at ν=10⁻⁷ (strictly within the singular band left unproved by Round 65), proving a₃,±(10⁻⁷)>0 and completely removing the dense-memory bottleneck. The remaining gap converges to the problem of G_n(ν)'s continuous-parameter extension/endpoint matching (STOP-C70), left for the next round's tangent-flow analysis; this round includes numerical verification scripts and CSV data.