feat(admin): phase 3 — dashboard #overview landing
GET /api/admin/overview returns 24h digest (~0.08ms/call).
- adminController.getOverview: 7 prepared statements (users 24h, sessions 24h, active users, classes count, failed sessions, banned this week, top-5 sessions)
- new section frontend/js/admin/sections/overview.js (~205L): bento-grid cards, alerts (only when >0), top-5 table, quick-links
- nav-item + tab-pane reordered: #overview is now default; #stats remains routable
Auth: admin-only (inside requireRole('admin') block, sibling of /stats).
Backward compat: all 13 existing routes unchanged.
Known follow-ups (post-merge polish):
- activeClasses counts all (label could be 'Всего классов')
- failedSessions24h includes in_progress (could tighten to abandoned only)
- topSessions24h drops NULL-score completed rows
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Maxim Dolgolyov
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