Use `git rev-parse --git-dir` instead of hardcoded `.git` path to find
the actual git directory. In worktrees, `.git` is a file containing a
gitdir pointer, not a directory.
Changes:
- Add getGitDir() helper in hooks.go
- Update installHooks(), uninstallHooks(), CheckGitHooks() to use it
- Update hooksInstalled(), detectExistingHooks(), installGitHooks() in init.go
- Update checkHooksQuick() in doctor.go
- Update GitHooks() in doctor/fix/hooks.go
- Update tests to use real git repos via `git init`
Fixes bd-63l
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
- Fix existing tests to work with new installHooks signature
- Add TestInstallHooksShared to verify shared hooks functionality
- Update git-hooks README with comprehensive --shared documentation
- Document benefits, use cases, and workflow for shared hooks
