feat(host_agent): surface network, disk I/O, and temperature in fleet widget

The agent already collects + ingests net throughput, disk I/O, and temps;
add them to the fleet-glance rows (fmt_bps + two-line io cells + temp with
70/85C threshold color), each shown only when the host reports it so VMs/
containers without sensors don't show blank cells.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plugins/host_agent/routes.py

@@ -409,6 +409,8 @@ async def _fleet_rows(session) -> list[dict]:
             "temp_max": m.get("temp_c_max"),
             "net_rx_bps": m.get("net_rx_bps"),
             "net_tx_bps": m.get("net_tx_bps"),
+            "disk_read_bps": m.get("disk_read_bps"),
+            "disk_write_bps": m.get("disk_write_bps"),
             "sparks": sparks,
         })
     rows.sort(key=lambda r: r["host"].name.lower())