feat(traffic): a host's top senders, on its page and as get_host_senders (#6115)

The host page gains a "Who's sending" panel, and the MCP a tool, that
put the host's outbound (or inbound) traffic down to its containers and
NFS mounts: read in shared time buckets, so the host's busiest bucket
says who was sending in it. A swarm service's tasks add up under its
name; what none of them accounts for is the host itself.

Also fixes CI 9488: per-container net_rx_bps / net_tx_bps join the
docker alert catalog, so a rule can catch a container flooding the
uplink.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugins/docker/__init__.py

@@ -89,10 +89,13 @@ def get_alert_metrics() -> dict[str, list[str]]:
     """What ingest.py records per container (resource "<host>/<container>"):
     restart_count is cumulative (alert on crash-looping); is_healthy is 1.0 /
     0.0 from the container's HEALTHCHECK, only for containers that define one.
+    net_rx_bps / net_tx_bps are the bytes a second it receives and sends
+    (#6115): "a container flooding the uplink" is net_tx_bps over a level.
     Per host (resource "<host>"), what Docker keeps on its disk (#5304).
     Swarm-wide (resource "swarm"), from any manager's report: services short
     of their replicas, nodes down and managers unreachable, drained nodes
     aside (#5788, swarm_health.py)."""
     from .disk_view import DISK_METRICS
     from .swarm_health import SWARM_METRICS
-    return {"docker": ["cpu_pct", "mem_used_pct", "restart_count", "is_healthy", *DISK_METRICS, *SWARM_METRICS]}
+    return {"docker": ["cpu_pct", "mem_used_pct", "restart_count", "is_healthy", "net_rx_bps", "net_tx_bps",
+                       *DISK_METRICS, *SWARM_METRICS]}