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>

steward/templates/hosts/overview_widget.html

@@ -1,4 +1,5 @@
 {# Unified Hosts widget — monitor status + agent glance per host, links to the hub. #}
+{% from "_macros.html" import metric_style %}
 {% if hosts %}
 <div style="display:grid;gap:0.1rem;">
   {% for host in hosts %}
@@ -10,10 +11,12 @@
   <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 down %}dot-down{% elif host.ping_enabled and ping %}dot-up{% else %}dot-dim{% endif %}"
           title="{% if not host.ping_enabled %}ping off{% elif ping %}{{ ping.status.value }}{% else %}no data{% endif %}"></span>
-    <a href="/hosts/{{ host.id }}"
-       style="flex:1;min-width:0;white-space:nowrap;overflow:hidden;text-overflow:ellipsis;font-weight:500;">
-      {{ 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/{{ host.id }}" title="{{ host.name }}" style="{{ name_style }}">{{ host.name }}</a>
+    {% else %}
+    <span title="{{ host.name }}" style="{{ name_style }}">{{ 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;">
       {# Monitors #}
       {% if host.ping_enabled and ping and ping.response_time_ms is not none %}
@@ -22,11 +25,11 @@
       {% if ut.get('24h') is not none %}
       <span title="Uptime 24h"><span style="color:var(--text-dim);">24h</span> {{ "%.1f"|format(ut['24h']) }}%</span>
       {% endif %}
-      {# Agent glance #}
+      {# Agent glance — failing metric coloured amber/red (≥80/≥90) #}
       {% if a %}
-      {% if a.get('cpu_pct') is not none %}<span title="CPU"><span style="color:var(--text-dim);">cpu</span> {{ "%.0f"|format(a.cpu_pct) }}%</span>{% endif %}
-      {% if a.get('mem_used_pct') is not none %}<span title="Memory"><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 (/)"><span style="color:var(--text-dim);">disk /</span> {{ "%.0f"|format(a.disk_root) }}%</span>{% endif %}
+      {% 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('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 %}
       {% else %}
       <span style="color:var(--text-dim);" title="No agent reporting">no agent</span>