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

cmd/bd/init.go

@@ -388,8 +388,8 @@ With --stealth: configures global git settings for invisible beads usage:
 		}
 
 		// Check if we're in a git repo and hooks aren't installed
-		// Install by default unless --skip-hooks is passed
-		if !skipHooks && isGitRepo() && !hooksInstalled() {
+		// Install by default unless --skip-hooks is passed or no-install-hooks config is set
+		if !skipHooks && !config.GetBool("no-install-hooks") && isGitRepo() && !hooksInstalled() {
 			if err := installGitHooks(); err != nil && !quiet {
 				yellow := color.New(color.FgYellow).SprintFunc()
 				fmt.Fprintf(os.Stderr, "\n%s Failed to install git hooks: %v\n", yellow("⚠"), err)