Codex Science v0.3.0 — Loop Engine

Adds a bounded plan → trace → eval → decision research improvement loop; explicit success, iteration, budget and stall gates; pinned third-party capability registry; static skill/plugin risk scanning with immutable checkout verification; automatic loop validation from the main project validator; loop evidence in research packets; and 12 lifecycle, negative, integrity and migration tests. External capabilities remain opt-in, revision-pinned and subject to separate runtime authorization.