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/ansible/bundled/host_agent/update.yml

@@ -1,5 +1,5 @@
 ---
-# description: Update the Steward host agent (refresh agent.py, its units and the maintenance helper, then restart) on hosts already running it.
+# description: Update the Steward host agent (refresh agent.py, its units, the maintenance helper and its packages, then restart) on hosts already running it.
 # steward:category: host-agent
 # Update an already-installed Steward host agent: refresh agent.py, its systemd
 # units and the maintenance helper (#5766), then restart.
@@ -66,6 +66,27 @@
         mode: "0755"
         force: true
 
+    # The helper's packages (smartctl for drive health, #5789), with whichever
+    # package manager the host has. One that can't be installed is said, never
+    # fatal: the host page then reads "smartctl not installed".
+    - name: Download the dependency installer
+      ansible.builtin.get_url:
+        url: "{{ steward_url }}/plugins/host_agent/files/install-deps.sh"
+        dest: /usr/local/lib/steward-agent/install-deps.sh
+        owner: root
+        mode: "0755"
+        force: true
+
+    - name: Install the helper's packages
+      ansible.builtin.command: /usr/local/lib/steward-agent/install-deps.sh
+      register: helper_deps
+      changed_when: "'installed:' in helper_deps.stdout"
+
+    - name: Say what couldn't be installed
+      ansible.builtin.debug:
+        msg: "{{ helper_deps.stdout_lines | select('search', 'WARNING') | list }}"
+      when: "'WARNING' in helper_deps.stdout"
+
     - name: Install the agent and maintenance units
       ansible.builtin.get_url:
         url: "{{ steward_url }}/plugins/host_agent/files/{{ item }}"