Phase 3 (convenience form) of golden-parity redesign (epic #2264). Adds npm run gen:golden (regenerates both fixture sets) and points the golden-parity/tree failure messages at it. Full CI-auto-comment deferred (documented in ADR-2264). Closes#2268.
Phase 2 of golden-parity redesign (epic #2264). Adds an install file-set snapshot (golden-install-tree) and a ci-test-scope rule selecting golden-parity whenever any installed-source path changes, closing the silent-staleness hole behind the #2266 red. ADR-2264 amended (the copy/transform split premise was unsound). Closes#2267.