feat(admin-dash): P0 — honest zeros, refresh+timestamp, hero hierarchy, stuck-sessions alert
- fmtNum: 0 no longer renders as "—" (muted "0" via .ov-zero instead)
- backend: classesTotal (renamed from activeClasses — was already full count, label fixed)
- backend: abandonedSessions24h (was failedSessions24h status!=completed; now only status=abandoned)
- backend: stuckSessions[] — in_progress > 1h with user/subject join, limit 5
- header: timestamp + manual refresh button (.ov-header flex layout), updates every 30s via interval
- newSessions24h card promoted to hero (2.6rem value, 52px icon, 2fr column ≥720px)
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Maxim Dolgolyov
64112e56ed