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>

steward/core/formatting.py

@@ -329,8 +329,9 @@ METRICS: dict[str, tuple[str, str]] = {
     "mem_used_pct": ("Memory used", "memory in use"),
     "mem_available_bytes": ("Memory available", "memory free for new work"),
     "swap_used_bytes": ("Swap used", "memory paged out to disk"),
-    "disk_used_pct_worst": ("Fullest disk", "the most-full mount on the host"),
+    "disk_used_pct_worst": ("Fullest disk", "the most-full mount on the host, by space or inodes"),
     "disk_used_pct": ("Disk used", "one mount (resource host:mount)"),
+    "inodes_used_pct": ("Inodes used", "one mount's file slots in use (resource host:mount); at 100% no file can be created"),
     "load_1m": ("Load (1 min)", "runnable processes, averaged over a minute"),
     "load_5m": ("Load (5 min)", "runnable processes, averaged over 5 minutes"),
     "load_15m": ("Load (15 min)", "runnable processes, averaged over 15 minutes"),