feat(dashboard): phase A widget clarity — threshold colours, host links, tooltips

Milestone 72 phase A (clarity wins, no schema change):
- Add shared metric_style() macro in _macros.html: colours a numeric metric
  amber (>=warn) / red (>=crit) on the value ITSELF, not just the status dot.
  Defaults 80/90 for percentage gauges; load /core uses warn 80 / crit 100.
  Applied to CPU/mem/disk across host_agent panel + fleet widget + the unified
  hosts-overview widget.
- Link every host reference to the host hub (/hosts/<id>) in ping, dns,
  hosts-overview, host_agent fleet, and uptime widgets; status widget entries
  link to their own detail_url. All guarded on session.user_id so the public
  share view degrades to plain text (the bare href carries no share token).
- Fix truncation: title= tooltips on all names that ellipsis, plus a hover
  underline affordance on the now-clickable ping-name links.

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

plugins/host_agent/templates/widget_table.html

@@ -1,4 +1,5 @@
 {# host_agent widget — fleet glance, flex rows (no header wrap) #}
+{% from "_macros.html" import metric_style %}
 {% if rows %}
 <div style="display:grid;gap:0.1rem;">
   {% for r in rows %}
@@ -6,19 +7,21 @@
   <div style="display:flex;align-items:center;gap:0.6rem;font-size:0.82rem;padding:0.3rem 0;border-bottom:1px solid var(--border);">
     <span class="dot {% if stale %}dot-dim{% elif (r.cpu_pct or 0) >= 90 or (r.mem_used_pct or 0) >= 90 or (r.disk_worst or 0) >= 90 %}dot-warn{% else %}dot-up{% endif %}"
           title="{% if stale %}stale / no recent data{% else %}warns at CPU/memory ≥90% or any disk mount ≥90% (the 'disk /' figure shows root only){% endif %}"></span>
-    <a href="/hosts/{{ r.host.id }}"
-       style="flex:1;min-width:0;white-space:nowrap;overflow:hidden;text-overflow:ellipsis;font-weight:500;">
-      {{ r.host.name }}
-    </a>
+    {% set name_style = "flex:1;min-width:0;white-space:nowrap;overflow:hidden;text-overflow:ellipsis;font-weight:500;" %}
+    {% if session.user_id %}
+    <a href="/hosts/{{ r.host.id }}" title="{{ r.host.name }}" style="{{ name_style }}">{{ r.host.name }}</a>
+    {% else %}
+    <span title="{{ r.host.name }}" style="{{ name_style }}">{{ r.host.name }}</span>
+    {% endif %}
     <span style="display:flex;gap:0.75rem;font-variant-numeric:tabular-nums;color:var(--text-muted);font-size:0.75rem;flex-shrink:0;">
       {% if r.cpu_pct is not none %}
-      <span title="CPU"><span style="color:var(--text-dim);">cpu</span> {{ "%.0f"|format(r.cpu_pct) }}%</span>
+      <span title="CPU" style="{{ metric_style(r.cpu_pct) }}"><span style="color:var(--text-dim);">cpu</span> {{ "%.0f"|format(r.cpu_pct) }}%</span>
       {% endif %}
       {% if r.mem_used_pct is not none %}
-      <span title="Memory"><span style="color:var(--text-dim);">mem</span> {{ "%.0f"|format(r.mem_used_pct) }}%</span>
+      <span title="Memory" style="{{ metric_style(r.mem_used_pct) }}"><span style="color:var(--text-dim);">mem</span> {{ "%.0f"|format(r.mem_used_pct) }}%</span>
       {% endif %}
       {% if r.disk_root is not none %}
-      <span title="Root filesystem (/) usage"><span style="color:var(--text-dim);">disk /</span> {{ "%.0f"|format(r.disk_root) }}%</span>
+      <span title="Root filesystem (/) usage" style="{{ metric_style(r.disk_root) }}"><span style="color:var(--text-dim);">disk /</span> {{ "%.0f"|format(r.disk_root) }}%</span>
       {% endif %}
       {% if r.load_1m is not none %}
       <span title="Load average 1m"><span style="color:var(--text-dim);">load</span> {{ "%.2f"|format(r.load_1m) }}</span>