The header status only considered recent-sync pending, so it read "all synced"
while the scheduler was still backfilling full history — directly contradicting
the adjacent "N without full history" notice. Add an active "fetching history"
state (spinner) shown when recent sync is done but deep backfill is still
pending, so "all synced" appears only when nothing is pending at all. The admin
pause button now also shows during deep backfill (it's pausable work). Trilingual.
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