Enum Layout SSOT & Take-Project Hardening

Centralize ALL enum layout knowledge into a single source of truth in ori_repr, migrate every codegen consumer to use that SSOT instead of hardcoded layout assumptions, harden the AIMS take-project ownership model against lineage gaps and iterator-only scope limitations, and replace weak source-text-only niche tests with emitter-driven IR verification — resolving 10 confirmed dual-source TPR findings from the repr-opt §07 architectural review and making the enum representation architecture sound for all current AND future layout optimizations (niche filling, payload compression, §08-§12 work).