feat(host_agent): a disk out of inodes reads as full (#5745)

VDNT-Util01's / ran out of inodes (956 free of 60.8M) with 274G of space
left; every file create failed and Steward's page read healthy at 66%.

- Agent 1.13.0 reports each mount's inodes (statvfs; a filesystem reporting
  none, like btrfs, is left without).
- Ingest records inodes_used_pct per mount, and disk_used_pct_worst is the
  fullest mount by space or inodes, so existing disk-full rules and the
  overview see it.
- The host's health strip, the Hosts widget and the host glance grade / by
  whichever is fuller and name inodes when they are ("Disk / 66% · inodes
  100%", "Inodes on / ... past its critical threshold").

Hosts pick up the inode figures once their agent is updated to 1.13.0.

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

plugins/host_agent/__init__.py

@@ -53,9 +53,11 @@ def get_alert_metrics() -> dict[str, list[str]]:
     comes from the scheduler, not the agent: "agent offline" is > 180.
     clock_off_secs is how far the host's clock is from Steward's, either way
     (agent ≥ 1.12.0): "clock drifting" is > 30. load_pct is load_1m as a %
-    of the host's cores."""
+    of the host's cores. inodes_used_pct is per mount (agent ≥ 1.13.0), and
+    disk_used_pct_worst is the fullest mount by space or inodes."""
     return {"host_agent": [
         "cpu_pct", "mem_used_pct", "mem_available_bytes", "swap_used_bytes",
-        "disk_used_pct_worst", "disk_used_pct", "load_1m", "load_5m", "load_15m", "load_pct",
+        "disk_used_pct_worst", "disk_used_pct", "inodes_used_pct", "load_1m", "load_5m", "load_15m",
+        "load_pct",
         "uptime_secs", "seconds_since_seen", "clock_off_secs",
     ]}