lint-fix-has-regression-test.cjs: new gate that fails if a fix(#NNNN)
or feat(#NNNN) commit has zero behavioral test files (*.test.cjs,
excluding auto-generated fixtures/baselines) in its diff. Wired into
lint:ci so it runs before PR creation.
Missing regression tests added:
- #2429: codex local scope does not set $HOME/.agents skills home;
global scope does (tests/runtime-artifact-layout.test.cjs)
- #2279: map-codebase instructions say to overwrite existing dates,
not just replace [YYYY-MM-DD] placeholders (tests/commands.test.cjs)
