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

internal/config/config.go

@@ -83,6 +83,7 @@ func Initialize() error {
 	v.SetDefault("db", "")
 	v.SetDefault("actor", "")
 	v.SetDefault("issue-prefix", "")
+	v.SetDefault("no-install-hooks", false)
 	
 	// Additional environment variables (not prefixed with BD_)
 	// These are bound explicitly for backward compatibility