Support env-driven service config on macOS

[dafacto]

Summary

• pass HOST, OPENCLAW_DIR, and OPENCLAW_BUNDLED_SKILLS_DIR into launchd/systemd service definitions
• include /opt/homebrew/bin in the default service PATH
• document that service env changes require rerunning ./setup.sh to rewrite the managed service

Verification

• verified launchd plist includes HOST=100.70.53.60, OPENCLAW_DIR, and OPENCLAW_BUNDLED_SKILLS_DIR
• confirmed live service is listening on 100.70.53.60:3333 on macOS
• ran ./update.sh --dry-run --skip-build --no-restart successfully from the updated branch

Created by Donna.