feat(host_agent): each drive's health, read with smartctl, alertable (#5789)

The root helper gains one read-only action, `drives`: it finds the drives
itself (smartctl --scan-open), reads each as JSON, and writes a summary the
agent carries on every sample (agent 1.20.0). Steward judges the figures in
drives.py (failing / worn / watch / ok / no SMART / unreadable), records them
per drive and as host roll-ups for covering rules, keeps the newest report on
the registration and lists it on the host page.

install-deps.sh installs smartmontools with apt, dnf, yum, zypper, pacman or
apk, run by install.sh and every agent playbook; one it can't install is
reported, never fatal.

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

steward/alerts/service.py

@@ -385,17 +385,19 @@ async def resources_for(db, source_module: str) -> list[str]:
 # A host's parts, by the shape of the name after "<host>:" (#5475): the order
 # and heading each kind takes in the rule form's Part picker.
 PART_KINDS = (("mount", "Mounts"), ("core", "CPU cores"), ("disk", "Disks"),
-              ("net", "Interfaces"), ("temp", "Temperatures"), ("other", "Other"))
+              ("drive", "Drive health"), ("net", "Interfaces"), ("temp", "Temperatures"),
+              ("other", "Other"))
 
 
 def part_kind(part: str) -> tuple[str, str]:
     """(kind, label) for a host part: "/var" is a mount, "core3" a core,
-    "diskio:sda" a disk, "net:eth0" an interface, "temp:Core 0" a sensor."""
+    "diskio:sda" a disk, "drive:sda" its health (#5789), "net:eth0" an
+    interface, "temp:Core 0" a sensor."""
     if part.startswith("/"):
         return "mount", part
     if part.startswith("core") and part[4:].isdigit():
         return "core", f"core {part[4:]}"
-    for prefix, kind in (("diskio:", "disk"), ("net:", "net"), ("temp:", "temp")):
+    for prefix, kind in (("diskio:", "disk"), ("drive:", "drive"), ("net:", "net"), ("temp:", "temp")):
         if part.startswith(prefix):
             return kind, part[len(prefix):]
     return "other", part