Add GET /api/admin/health powered by a config health service that
detects common deployment mistakes: missing or read-only data volume,
broken tariffs/locale-override/guides JSON files, payment providers
enabled without credentials, webhook providers without
WEBHOOK_BASE_URL, no enabled payment methods, missing or non-https
mini app URL, missing Redis, partially configured SMTP, untrusted
reverse proxy, invalid bot token, missing/mismatched/failing Telegram
webhook and unreachable Remnawave panel. Network checks (Telegram,
panel) are cached for two minutes; ?refresh=1 forces a re-check.
The admin UI shows the alerts as a banner on the dashboard with
per-section navigation chips and a manual re-check button, and as a
filtered banner inside each affected section. Alerts are localized
via admin_health_* keys with built-in Russian fallbacks.
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