Pre-commit hook runs lint+fmt-check, not full check (TDD)

Tests are deliberately excluded from the pre-commit hook so that the
TDD red-phase commit (failing tests landing before implementation) can
land on a feature branch. CI still runs full make check via docker build
so a red branch cannot reach main.

README.md

@@ -90,6 +90,11 @@ All work on quack is test-driven. No exceptions.
    test-then-implementation sequence into reviewable commits, but the final
    history must still show tests landing before (or with) the matching
    implementation.
+8. The pre-commit hook installed by `make hooks` runs
+   `make lint && make fmt-check`, not the full `make check`. This is deliberate
+   so the TDD red-phase commit (failing tests, no implementation yet) can land.
+   The full `make check` runs as part of `docker build .`, which is what CI
+   executes, so a red branch still cannot reach `main`.
 
 ## Design