Primitive Factorisation of the Evans Lattice Zeta

Research Note 38 in the "Geometry of the Critical Line" programme. This note proves a canonical factorisation of the leading-WKB Evans lattice zeta. The integer scaling action (n, m') → (dn, dm') partitions the lattice into primitive orbits (gcd (n, m') = 1) and their integer multiples. Standard Möbius inversion gives ZEvans (s) = ζ (2s) · Zₚrim (s), where Zₚrim is the primitive lattice zeta and ζ (2s) is the Riemann zeta function at argument 2s. The factorisation is verified numerically to six significant figures. It shows that the Riemann zeta function is already present as the common-scaling multiplicity factor of the Evans lattice. The geometric factor Zₚrim (s) carries the pole at s = 1; the arithmetic factor ζ (2s) carries the pole at s = 1/2. The factorisation identifies where the arithmetic content lives inside the carrier geometry, but does not by itself extract it — that requires the operator-algebraic quotient.