deploy: resumable copies, and a runner drop-in that cannot starve the host !167

install.sh and make deploy-runner copy with rsync --partial --inplace -z (scp -C fallback in install.sh). deploy/gitbay-runner.override.conf adds Nice=10, CPUWeight=30, IOWeight=30 as a drop-in, installed by make deploy-runner with a daemon-reload.

Shell and Makefile only; no Go changes.