Fix GH#254: bd init now detects and chains with existing git hooks

- Detect existing git hooks (pre-commit framework, custom scripts)
- Prompt user with 3 options: chain (recommended), overwrite, skip
- Chain mode preserves existing hooks by calling them first
- Overwrite mode creates timestamped backups
- Add tests for hook detection and installation
- Update documentation with chaining feature

Fixes silent overwrites of pre-commit framework hooks that caused
test failures to slip through.

Amp-Thread-ID: https://ampcode.com/threads/T-37164fd7-6452-40b0-b5dd-c13672dcb843
Co-authored-by: Amp <amp@ampcode.com>

examples/git-hooks/README.md

@@ -28,7 +28,7 @@ These git hooks ensure bd changes are always synchronized with your commits and
 
 ## Installation
 
-### Quick Install
+### Quick Install (Recommended)
 
 From your repository root:
 
@@ -36,10 +36,20 @@ From your repository root:
 ./examples/git-hooks/install.sh
 ```
 
-This will:
+Or use `bd init --quiet` to install hooks automatically.
+
+**Hook Chaining (New in v0.23):** If you already have git hooks installed (e.g., pre-commit framework), bd will:
+- Detect existing hooks
+- Offer to chain with them (recommended)
+- Preserve your existing hooks while adding bd functionality
+- Back up hooks if you choose to overwrite
+
+This prevents bd from silently overwriting workflows like pre-commit framework, which previously caused test failures to slip through.
+
+The installer will:
 - Copy hooks to `.git/hooks/`
 - Make them executable
-- Back up any existing hooks
+- Detect and preserve existing hooks
 
 ### Manual Install