install: replace deploy/upgrade with smart install-service
Single install-service target detects fresh-install vs upgrade via a
~/.config/solstone-linux/.install-source marker and runs CI in upgrade mode.
Marker ownership guard hard-fails on cross-repo contamination and on
pre-hygiene installs with no marker; manual remediation is the documented
recovery path. Drop the --force flag and Unit-unchanged short-circuit from
cmd_install_service — the unit is content-equivalent across clones so
unconditional rewrite is the simpler model.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>