feat(config): add BD_NO_INSTALL_HOOKS environment variable to disable git hook installation (#500)

* feat(config): add no-install-hooks config to disable git hook installation

Add `no-install-hooks` boolean config that prevents git hook installation
during `bd init`. This can be set via:
- Environment variable: BD_NO_INSTALL_HOOKS=1
- Global config: ~/.config/bd/config.yaml with `no-install-hooks: true`
- Local config: .beads/config.yaml with `no-install-hooks: true`

The existing `--skip-hooks` flag continues to work and takes precedence.
Default behavior unchanged: hooks install by default.

* docs: add no-install-hooks to configuration documentation

- Add no-install-hooks to Supported Settings table in CONFIG.md
- Add example in config file section
- Add "Disabling Hook Installation" section to GIT_INTEGRATION.md
  with examples for flag, env var, and config file methods

docs/GIT_INTEGRATION.md

@@ -251,11 +251,33 @@ See [PROTECTED_BRANCHES.md](PROTECTED_BRANCHES.md) for complete setup guide, tro
 
 ### Installation
 
+Git hooks are installed automatically during `bd init`. To install manually:
+
 ```bash
 # One-time setup in each beads workspace
 ./examples/git-hooks/install.sh
 ```
 
+### Disabling Hook Installation
+
+If you prefer to manage git hooks separately (e.g., using pre-commit, husky, or your own hook manager), you can disable automatic hook installation:
+
+```bash
+# Via command-line flag
+bd init --skip-hooks
+
+# Via environment variable (useful for CI/scripts)
+BD_NO_INSTALL_HOOKS=1 bd init
+
+# Via global config (~/.config/bd/config.yaml)
+no-install-hooks: true
+
+# Via project config (.beads/config.yaml)
+no-install-hooks: true
+```
+
+**Precedence:** `--skip-hooks` flag > `BD_NO_INSTALL_HOOKS` env var > config file > default (install hooks)
+
 ### What Gets Installed
 
 **pre-commit hook:**