M5 — Gameplay and world migration

Migrate every preserved gameplay, progression, world, client, and authored-content behavior onto native Go, compiled data/CEL, and Rust applications; eliminate runtime Python and close all parity inventories without redesigning the game. Exit: atrinik#280 proves whole-baseline-content-pack functional equivalence with zero unowned required rows. Authoritative plan: atrinik/atrinik#168.