chore: consolidate install-git-hooks.sh (bash) and install-hooks.js (node) into single source

[CodeMonkeyCybersecurity]

Summary

There are now two hook installation mechanisms:

1. scripts/install-git-hooks.sh (403 lines, bash, original)
2. scripts/install-hooks.js (new, node, installed via npm postinstall)

These should be consolidated to avoid drift. Recommend keeping the Node.js version since it's wired into npm postinstall and the project is moving to npm-based tooling.

Acceptance Criteria

• Single hook installation mechanism
• npm install automatically installs hooks (postinstall)
• Hooks are functionally equivalent
• Remove deprecated script