add cross-platform background service management (sol service, sol up/down)
New module think/service.py provides install/uninstall/start/stop/restart/status/logs
subcommands for managing solstone as a persistent user-level background service via
launchd (macOS) or systemd --user (Linux). sol up/down aliases provide quick access.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>