feat(make): add upgrade (CI-gated) and service-logs targets
make upgrade runs ci, then restarts the installed service (no-op in dev via --if-installed).
make service-logs wraps sol service logs -f for cross-platform log tailing.
make sail is preserved unchanged. Adds verb parity with solstone-linux and solstone-tmux.
Also adds an "updating after a code change" section to INSTALL.md documenting git pull && make upgrade and the CI gate.