fix: set core.hookspath in prepare script to override global config

[cs01]

Summary

• The prepare script now sets git config core.hooksPath .git/hooks before copying the pre-commit hook
• Fixes: global core.hooksPath (e.g. from a previous husky install) silently overrides the repo's hook directory, so npm install installs the hook but git never runs it
• The pre-commit hook auto-formats staged .ts/.js files with prettier — prevents format-check CI failures

Test plan

• npm run prepare succeeds and installs hook
• Commits from worktrees trigger the pre-commit hook

🤖 Generated with Claude Code