fix(hooks): warn when preserved pre-commit hook does not dispatch pre-commit.d (#52)

[olavostauros]

Summary

When install-hooks or setup preserves an existing custom pre-commit hook that does not dispatch pre-commit.d/, print a warning explaining that the modules guards were installed but may not run.

The heuristic uses grep -q 'pre-commit\.d' — simple, catches the vast majority of real dispatchers, and false positives are harmless warnings.

Closes #52

Changes

File	Change
lib/hooks.sh	Added elif branch in install_pre_commit_hooks — warns when preserved hook doesn't mention pre-commit.d
test/hooks.bats	2 new tests: warning fires for non-dispatching hook, stays quiet for dispatching hook

Validation

• mise run test — 138/138 passing
• codebase lint "$PWD"
• git diff --check