* feat: add system monitor panel with live CPU, memory, disk, and GPU metrics
New btop-inspired monitoring page in the OBSERVE sidebar group.
Polls /api/system-monitor every 2s and renders rolling Recharts area
charts for CPU/memory/GPU and progress bars for disk usage.
* feat: add network I/O monitoring to system monitor panel
Add live network throughput (rx/tx bytes/sec) as a dual area chart.
API returns cumulative byte counters per interface (stateless), frontend
computes rates from deltas between 2s polls. Supports Linux (/proc/net/dev)
and macOS (netstat -ib).
* feat: add top processes list to system monitor
Shows top 8 processes by CPU usage in a compact table with CPU%, Mem%,
and RSS columns. Color-codes high usage values. Uses ps on both Linux
and macOS with fallback for platforms without --sort support.
* fix: normalize process CPU% to 0-100 and filter out ps itself
CPU% from ps is per-core (e.g. 200% on 4 cores), now divided by core
count to show total system percentage. Also filters out the ps command
that briefly appears while collecting process data.
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Co-authored-by: Dan <github@bookkept.com.au>
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