Polynomial Closure - v0.2

v0.2: polynomial closure on four integers + recursive echo ledger

Replace the E8/ per-layer package (14 modules) with interference/
(7 flat modules + run + words). Every dimensionless quantity is now
a polynomial or rational function of four irreducible integers
(d_10=2, d_11=3, n_7=7, n_26=26) + pi, with m_e as the sole
dimensional anchor (M_Pl, G, v_EW, m_mu, m_tau become outputs).
The four-integer rigidity is proven in the companion paper
"The Octavian Coherence Gate" (doi:10.5281/zenodo.20493955).

Deeper interference layers are tracked by one recursion
x_{t+1} = b + W(x_t), implemented as the EchoTerm/Ledger/Web
machinery in root.py. The Hurwitz gate caps echo depth at 3
(matching R -> C -> H -> O), so every derived edge is a theorem
in the four integers and no numerology can enter the recursion.

New predictions: sin^2 theta_W, M_W, M_Z (electroweak triplet) and
Omega_DM/Omega_b = 2pi - 1. Scorecard: 35 numerical checks + 3
structural closures. 58 pytest tests, run from repo root.

Also fixes the Perron-Frobenius eigenvalue assertion in words.py
(the D^(6) nimrep has three magnitude-2 eigenvalues, so the
real-eigenvalue filter is required).