ReadWritePaths was missing the install target dir, so self-upgrade cp'd
against a ProtectSystem=strict read-only mount even via sudo. Added
${INSTALL_DIR} to the template and /usr/local/bin to the Go installer
constant.
queueSystemHeartbeat now writes heartbeat_source=system to agent metadata,
mirroring the pattern in TriggerHeartbeat / triggerSystemHeartbeat, so
GetHeartbeatStatus returns the correct source and the dashboard renders
the blue indicator for system-initiated heartbeats.
eac47f8826