fix(dashboard): inline cpu sparkline, history graph host label + stable y-axis

- Hosts-Overview: move the CPU sparkline inline next to the cpu % value it
  represents (was floated far right on the name line, reading as unrelated).
- Host Agent history widget: caption the chart with the host it represents
  (the panel title is generic) — links to the host hub.
- History widget: snap the y-axis to a stable 0..next-10%-band ceiling instead
  of auto-scaling to the exact peak, so the 'zoom' no longer jumps each poll.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

steward/templates/hosts/overview_widget.html

@@ -22,7 +22,6 @@
       {% else %}
       <span style="font-weight:600;font-size:0.85rem;overflow-wrap:anywhere;">{{ host.name }}</span>
       {% endif %}
-      {% if spark %}<span title="CPU — last hour" style="margin-left:auto;line-height:0;opacity:0.85;flex-shrink:0;">{{ spark | safe }}</span>{% endif %}
     </div>
     {# Line 2 — monitors + agent metrics; wraps instead of truncating #}
     <div style="display:flex;flex-wrap:wrap;gap:0.25rem 0.9rem;margin-top:0.25rem;padding-left:1.1rem;
@@ -34,7 +33,7 @@
       <span title="Uptime 24h"><span style="color:var(--text-dim);">24h</span> {{ "%.1f"|format(ut['24h']) }}%</span>
       {% endif %}
       {% if a %}
-      {% if a.get('cpu_pct') is not none %}<span title="CPU" style="{{ metric_style(a.cpu_pct) }}"><span style="color:var(--text-dim);">cpu</span> {{ "%.0f"|format(a.cpu_pct) }}%</span>{% endif %}
+      {% if a.get('cpu_pct') is not none %}<span title="CPU — value + last-hour trend" style="display:inline-flex;align-items:center;gap:0.3rem;{{ metric_style(a.cpu_pct) }}"><span style="color:var(--text-dim);">cpu</span> {{ "%.0f"|format(a.cpu_pct) }}%{% if spark %}<span style="line-height:0;opacity:0.85;">{{ spark | safe }}</span>{% endif %}</span>{% endif %}
       {% if a.get('mem_used_pct') is not none %}<span title="Memory" style="{{ metric_style(a.mem_used_pct) }}"><span style="color:var(--text-dim);">mem</span> {{ "%.0f"|format(a.mem_used_pct) }}%</span>{% endif %}
       {% if a.get('disk_root') is not none %}<span title="Root filesystem (/)" style="{{ metric_style(a.disk_root) }}"><span style="color:var(--text-dim);">disk /</span> {{ "%.0f"|format(a.disk_root) }}%</span>{% endif %}
       {% if not a.fresh %}<span title="Agent data is stale" style="color:var(--yellow);">stale</span>{% endif %}