Surfaces the metrics the agent now collects (task #868). Adds a viewer-facing
fleet page (/plugins/host_agent/) with per-host cards (CPU/mem/disk/load/temp,
stale flag) and a per-host detail page (/plugins/host_agent/<id>/) — the link
the fleet widget already pointed at but had no route for.
Detail page shows current gauges (CPU, memory incl. swap/cache, load, network
rx/tx, disk I/O, temp max, memory/cpu/io PSI), per-core CPU bars, per-mount
filesystem bars, and per-interface/disk/sensor breakdowns, plus history charts
(utilization %, throughput B/s, load & pressure) over a selectable range.
Charts use a linear epoch-ms x-axis so no Chart.js date adapter is needed.
Stale state uses the plugin's stale_after_seconds threshold. Repoints the
host_resources widget detail link from admin settings to the new fleet page.
Completes milestone #68 (task #867).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
