the rational-angle lock

Adds papers/rational_angle_lock.md and code/verify_angle_lock.py. The note closes the one item the fourth paper flagged as possibly carrying content beyond bookkeeping — the rational-angle locking of the Toeplitz symbol's minimum — by identifying the edge law as the Hardy–Littlewood singular series μ(q)/φ(q) multiplying a Lerch–Wood polylogarithm cusp, i.e. the major arcs of the circle method. Rescaling every measured edge by φ(q)/μ(q) collapses them onto one prime-free universal cusp (mean 0.9944, sd 0.0096).

Corrects a number in the fourth paper: the handover from θ = π to θ = 2π/5 is at α* = 0.74005083, not "about α = 0.71". Appendix A item 2 is marked answered in place, with the correction recorded rather than silently edited.

Housekeeping: removes AI_disclosure.md, a working file committed to the repo root by mistake; unifies the AI-assistance line across all seven documents (paper vs note, with a pointer to the fuller statement in the README); brings .zenodo.json and CITATION.cff up to date with the notes added in v1.9.