Runner-job metrics charts are aligned, complete, and time-correct

Three fixes make the runner-job machine-metrics charts trustworthy end-to-end. The chart’s x-axis is now anchored to the job’s step window, so hovering a step highlights the right point on the timeline instead of drifting toward the middle or off the right edge. Runner service-account token TTL is bumped from 1h to 8h, so long jobs no longer hit 401 mid-run after the token expired and have their charts cut off partway through. And freshly booted macOS runner VMs now run a forced clock step before the job starts, so early GitHub step timestamps and the macOS metrics sampler finally sit on the same timeline.