feat: UI redesign (CSS system, DNS widget, Traefik dashboard widget)

- Replace base.html style block with full CSS design system using custom properties (dark theme, cards, tables, badges, dots, widgets)
- Add DNS blueprint (fablednetmon/dns/) with /dns/ and /dns/rows routes + templates
- Add Traefik /widget route and widget.html fragment for dashboard
- Update dashboard: DNS + Traefik widgets, traefik_enabled config detection
- Update all templates to use new CSS classes (page-title, section-title, card-flush, table, badge-*, dot-*, btn-*)
- Register dns_bp in app.py

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

fablednetmon/templates/dns/rows.html

@@ -0,0 +1,29 @@
+{% if hosts %}
+{% for host in hosts %}
+{% set d = latest.get(host.id) %}
+<div class="ping-row">
+  <div class="ping-meta">
+    <span class="ping-name">{{ host.name }}</span>
+    <span class="ping-addr">{{ host.address }}</span>
+  </div>
+  <div style="flex:1;">
+    {% if d is none %}
+      <span style="color:var(--text-dim);font-size:0.85rem;">—</span>
+    {% elif d.status.value == 'resolved' %}
+      <span class="dot dot-up" style="margin-right:0.5rem;"></span>
+      <span style="font-size:0.85rem;color:var(--green);">{{ d.resolved_ip or 'resolved' }}</span>
+    {% else %}
+      <span class="dot dot-down" style="margin-right:0.5rem;"></span>
+      <span style="font-size:0.85rem;color:var(--red);">Failed</span>
+    {% endif %}
+  </div>
+  <div class="ping-cur">
+    {% if d %}
+      <span style="color:var(--text-muted);font-size:0.75rem;">{{ d.resolved_at.strftime('%H:%M:%S') }} UTC</span>
+    {% endif %}
+  </div>
+</div>
+{% endfor %}
+{% else %}
+<p class="empty" style="padding:0.5rem 0;">No DNS-enabled hosts. <a href="/hosts/">Enable DNS on a host →</a></p>
+{% endif %}