feat(doctor): detect external hook managers and check bd integration (#908)

Add detection for external git hook managers (lefthook, husky, pre-commit,
overcommit, yorkie, simple-git-hooks) and check if they have bd hooks
integration configured.

- Detect manager config files in various locations/formats
- Parse lefthook YAML/TOML/JSON to check for `bd hooks run` commands
- Check husky hook scripts for bd integration
- Report which hooks have bd integration vs missing
- Use --chain flag in `bd doctor --fix` when external managers detected
- Detect active manager from git hooks when multiple present

Executed-By: mayor
Role: mayor

CHANGELOG.md

@@ -5,6 +5,17 @@ All notable changes to the beads project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Added
+
+- **External hook manager detection** - `bd doctor` now detects lefthook, husky, pre-commit, and other hook managers
+  - Checks if external managers have `bd hooks run` integration configured
+  - Reports which hooks have bd integration vs which are missing
+  - `bd doctor --fix` uses `--chain` flag when external managers detected to preserve existing hooks
+  - Supports YAML, TOML, and JSON config formats for lefthook
+  - Detects active manager from git hooks when multiple managers present
+
 ## [0.44.0] - 2026-01-04
 
 ### Added