Adds wiki/concepts.yaml (5 curated seeds: discrete-conformal-map, circle-packing, lobachevsky-function, discrete-yamabe-flow, hyperideal-tetrahedron) and codex/wiki.py with full load_concepts() implementation (Concept dataclass, YAML parser, graceful empty list). Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>