GWTC-4.0: An Introduction to Version 4.0 of the Gravitational-Wave Transient Catalog - The LIGO Scientific Collaboration; the Virgo Collaboration; the KAGRA Collaboration; Abac, A. G.; Abouelfettouh, I.; Acernese, F.; Ackley, K.; Adhicary, S.; Adhikari, D.; Adhikari, N.; Adhikari, R. X.; Adkins, V. K.; et al. (2025)