The grep-output-truncator hook was never registered in index.ts, so grep
output was not being truncated since commit 03a4501 which removed grep/Grep
from tool-output-truncator's TRUNCATABLE_TOOLS list.
- Remove unused grep-output-truncator.ts
- Add "grep" and "Grep" back to tool-output-truncator's TRUNCATABLE_TOOLS
Co-authored-by: Claude <noreply@anthropic.com>