Implement Dashboard Metrics Cards

**Description:**

- Display main platform metrics:
- Total users
- Active users
- Total servers
- Messages (24h / 7d)

Use shadcn Card components.

**Checklist:**

- [ ] Create StatCard component
- [ ] Fetch metrics from API
- [ ] Display loading state
- [ ] Display error state

Start by locating the dashboard entry point, the existing API client, and examples of shadcn Card usage. Define how the metrics response maps to Total users, Active users, Total servers, and Messages for 24h/7d, then verify loading and error states. Done means a StatCard-based dashboard displays all metrics and handles both request states.

Written by the indexing model from the issue text.