Implement Real-Time Metrics Collection in Admin Dashboard

[Steake]

Part of Epic: #71 - RC1: Zero-Knowledge & Observability

---

Goal: Populate dashboard with real network and system metrics—including uptime, peer count, block height, resource usage and trust scores.

Requirements:

• Inject real node/network metrics data into admin API endpoints
• Calculate uptime, block times, peer count, trust scores, slashing events, CPU/RAM/disk metrics
• Remove mock values, display actual metrics in dashboard

Files:

• crates/bitcell-admin/src/api/metrics.rs

Acceptance Criteria:

• Dashboard visualizes live node and chain status
• Real trusted metrics for node operation

See todo_now.md.

[Steake]

[autopilot] @copilot please start work on this issue and open a PR that references #41 in the PR description.