v0.2.4 — config file support

• Configure auto-background threshold with ~/.pi-background-bash/config.json.\n- Project overrides via .pi/background-bash.json.\n- Adds Lefthook local pre-commit config for npm test.\n- Removes documented env-var configuration.\n\nInstall:\n\nbash\npi install git:github.com/sshkeda/pi-background-bash@v0.2.4\n\n\nVerified with npm test / pi-mock: 11 passing.