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/status/widget.html

@@ -15,7 +15,13 @@
   {% for e in problems[:8] %}
   <div style="display:flex;align-items:center;gap:0.5rem;padding:0.2rem 0;font-size:0.82rem;">
     <span class="dot {% if e.status == 'down' %}dot-down{% else %}dot-dim{% endif %}"></span>
-    <span style="flex:1;min-width:0;white-space:nowrap;overflow:hidden;text-overflow:ellipsis;">{{ e.name }}</span>
+    {% set nm_style = "flex:1;min-width:0;white-space:nowrap;overflow:hidden;text-overflow:ellipsis;" %}
+    {# Link to the monitor's own detail view for logged-in users; plain text on the public share view. #}
+    {% if session.user_id and e.detail_url %}
+    <a href="{{ e.detail_url }}" title="{{ e.name }}" style="{{ nm_style }}color:inherit;text-decoration:none;">{{ e.name }}</a>
+    {% else %}
+    <span title="{{ e.name }}" style="{{ nm_style }}">{{ e.name }}</span>
+    {% endif %}
     <span style="color:var(--text-dim);font-size:0.7rem;text-transform:uppercase;">{{ e.kind }}</span>
     <span style="color:{% if e.status == 'down' %}var(--red){% else %}var(--yellow){% endif %};font-size:0.75rem;font-weight:600;">{{ e.status }}</span>
   </div>