Address the /code-review findings on the tag cell:
- key the overflow-fit measurement on tag id+name so a RENAME (which changes chip
width) re-runs the fit, not just add/remove;
- reserve the '+N' pill space using the MEASURED gap (gap-1 is rem, scales with the
font slider) instead of a px constant;
- force the reveal-all hover popover's state closed when nothing is collapsed, so it
can't linger open against an unmounted '+N' trigger.