[Admin][UI] Overview dashboard #36

[Admin][UI] Overview dashboard

Why

The landing page: an at-a-glance operator health + KPI view.

Scope

• Stat cards: total users, total agents (published/draft), active instances, 24h AI calls, 30-day platform-paid spend $, 24h errors.
• Trend chart (custom SVG, no chart lib — matches console/PAS): usage or spend over last 14–30 days.
• Ops summary strip: stuck/failed sessions count, no-key users, error spikes (from the Ops endpoint) with a link to Errors & Ops.
• Top lists: top agents by instances, top spenders.

Acceptance criteria

• Cards + trend render from /v1/admin/spending + /v1/admin/usage + counts.
• Platform-paid spend is prominent (the headline number).
• Loading/empty/error states handled.

Relevant code

• store/admin/ Overview page; consumes Usage/Spending + Ops APIs.

References

• FGS Overview, PAS PlatformAnalyticsPanel.tsx (SVG charts).

Part of the PAGS Admin Portal epic. Depends on UI scaffold + the Usage/Spending & Ops APIs.