fix(concurrency): silent background refresh — no loading flicker

The 2s status poll (and post-mutation limit reloads) toggled a visible
loading state, but since the refresh is near-instant the spinner flashed
for <1 frame — a visible flicker/jerk every poll. The polling is now
SILENT (mirrors the heartbeat runs list):

- refreshLimits/refreshStatus: re-entrancy guard (limitsInFlight/statusInFlight,
  no UI), no loading-state toggle. Error cleared only on success so it stays
  visible + stable during an in-flight retry (no vanish-mid-poll).
- Removed limitsLoading/statusLoading: the Refresh buttons are plain-text
  (no spinner, not disabled); the empty-state guards use hasLoaded* only
  (no && !loading), so the list area never reflows mid-refresh.

+1 regression-guard test (Refresh buttons never surface a spinner). typecheck
0/0, 926 tests green (x2), biome clean, build OK.

0 files changed, 0 insertions, 0 deletions