feat(hosts): true live vitals strip; agent panel becomes management-only

Realizes the chosen host-summary layout: a thin live vitals bar at the very top,
separate from the agent management panel (no more duplicated CPU/MEM/DISK/LOAD).

- New fragment _host_vitals.html + route /plugins/host_agent/vitals/<id>: compact
  CPU / Memory / Disk(/) / Load-per-core (threshold-coloured + sparkline) +
  Pressure + live/stale·version·last-seen. Polled every 15s; renders nothing
  until the agent reports.
- The metric computation (latest snapshot + 6h sparkline query + load/core + PSI)
  moves from host_panel into host_vitals. host_panel slims to management only
  (reg/target/reporting/stale/ansible) and no longer queries metrics; panel.html
  drops the gauge row + pressure block, keeping status + lifecycle actions.
- hosts/detail.html: vitals strip on top (full width, live), then a 2-col
  [Monitors | Agent] grid, Ansible full width below, docker fragment last.

UI only. Templates parse; plugin-template parse test covers the new fragment.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016Jg27rgypiW2efULXJDtMC

plugins/host_agent/templates/panel.html

@@ -14,39 +14,8 @@
   </div>
 
   {% if reporting %}
-  {# ── Reporting: at-a-glance metrics (+ sparkline trend) + lifecycle ── #}
-  {% set cpu = hostlvl.get('cpu_pct') %}
-  {% set mem = hostlvl.get('mem_used_pct') %}
-  {% set lbl = "font-size:0.72rem;color:var(--text-muted);text-transform:uppercase;" %}
-  <div style="display:flex;gap:1.5rem;flex-wrap:wrap;margin-bottom:0.6rem;">
-    <div title="Average CPU utilization across all cores">
-      <div style="{{ lbl }}">CPU</div>
-      <div style="font-weight:600;{{ threshold_style(cpu, 'cpu') }}">{{ '%.0f%%'|format(cpu) if cpu is not none else '—' }}</div>
-      {{ sparks.cpu | safe }}</div>
-    <div title="RAM in use (total minus available; cache/buffers count as free)">
-      <div style="{{ lbl }}">Memory</div>
-      <div style="font-weight:600;{{ threshold_style(mem, 'mem') }}">{{ '%.0f%%'|format(mem) if mem is not none else '—' }}</div>
-      {{ sparks.mem | safe }}</div>
-    <div title="Root filesystem (/) usage — see Full metrics for every mount">
-      <div style="{{ lbl }}">Disk /</div>
-      <div style="font-weight:600;{{ threshold_style(disk_root, 'disk') }}">{{ '%.0f%%'|format(disk_root) if disk_root is not none else '—' }}</div>
-      {{ sparks.disk | safe }}</div>
-    {# Load /core: 100% = run queue matches CPU capacity, so warn 80 / crit 100. #}
-    <div title="1-minute load average ÷ {{ cores or '?' }} CPU cores (100% = run queue matches capacity). Raw 1m load: {{ '%.2f'|format(load1) if load1 is not none else '—' }}.">
-      <div style="{{ lbl }}">Load /core</div>
-      <div style="font-weight:600;{{ threshold_style(load_per_core, 'load') }}">{{ '%d%%'|format(load_per_core) if load_per_core is not none else ('%.2f'|format(load1) if load1 is not none else '—') }}</div>
-      {{ sparks.load | safe }}</div>
-  </div>
-  {% if psi.cpu is not none or psi.mem is not none or psi.io is not none %}
-  <div style="font-size:0.75rem;color:var(--text-muted);margin-bottom:0.9rem;"
-       title="Pressure Stall Information — % of the last 10s that tasks were stalled waiting for the resource. Hardware-independent, comparable across hosts.">
-    <span style="text-transform:uppercase;font-size:0.7rem;letter-spacing:0.04em;color:var(--text-dim);">Pressure 10s</span>
-    &nbsp;CPU {{ '%.0f%%'|format(psi.cpu) if psi.cpu is not none else '—' }}
-    · Mem {{ '%.0f%%'|format(psi.mem) if psi.mem is not none else '—' }}
-    · IO {{ '%.0f%%'|format(psi.io) if psi.io is not none else '—' }}
-  </div>
-  {% endif %}
-
+  {# Reporting: live vitals are shown by the vitals strip above; this panel is
+     lifecycle/management only. #}
   <div style="display:flex;gap:0.5rem;flex-wrap:wrap;align-items:center;">
     <a href="/plugins/host_agent/{{ host.id }}/" class="btn btn-sm btn-ghost">Full metrics →</a>
     {% if session.user_role == 'admin' %}