Does AI Help? October 2026, version 2026.10.11

Adds the Leiden Declaration on Artificial Intelligence and Mathematics with 16 registered authors, original 2 June 2026 date, Zenodo DOI and separate arXiv version history. Verified IMU endorsement and added qualified mathematical-governance context, distinct from empirical productivity findings. Updated evidence exports, web article and PDF. Cutoff remains 13 October 2026; previous release archives are preserved.