The daemon was called with --config pointing at the .runner registration
state file (JSON), not a YAML config. act_runner rejected it immediately
on every start, so all runners were always offline and never reconnected.
Also fix log truncation and stale fallback labels.
- rootfs/usr/local/bin/start-runners: remove --config from act_runner
daemon invocation (act_runner finds .runner in CWD automatically after
cd "$runner_dir"); fix __log to append (>>) instead of truncate (>);
update fallback RUNNER_LABELS to match the full label set defined in
zz-act_runner.sh
rootfs/usr/local/bin/start-runners