#1365 Dashboard - metrics logs

Description

## Title
serve: the Monitor's values are saved to logs/metrics.jsonl and shown as live charts at /metrics-history

Issue: Resolves #1364

## Summary
The Monitor tab only shows the last minute of values and keeps nothing once the page closes. With this change the
server writes every value the Monitor shows to a JSONL file once a second, whether or not a browser is open. A new
page, `/metrics-history`, draws that file as live line charts, so you can see how speed, VRAM, PCIe, power and the
other values moved during a task. No prompts or answers are written.

<img width="1920" height="900" alt="Screenshot 2026-10-05 133545" src="https://github.com/user-attachments/assets/c81b4665-83a0-4d68-9be0-3ab90ff330e1" />