Add a lightweight regression for the documented local pre-push build gate so the skip hatch and lockfile-grade cargo build command stay aligned with operator docs.
Constraint: Issue #696 scope is limited to pre-push hook contract drift after ROADMAP #694.\nRejected: Reworking the hook harness or roadmap board | unnecessary for the focused drift guard.\nConfidence: high\nScope-risk: narrow\nDirective: Keep the hook docs, skip hatch, and cargo --locked command in sync when changing local push gates.\nTested: bash -n .github/hooks/pre-push; python3 tests/test_pre_push_hook_contract.py -v; git diff --check\nNot-tested: Full cargo workspace build; Rust code was not touched.
