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/hosts/form.html

@@ -2,7 +2,7 @@
 {% block title %}{% if host %}Edit Host{% else %}New Host{% endif %} — FabledNetMon{% endblock %}
 {% block content %}
 <div style="max-width:560px;margin:2rem auto;">
-    <h1 style="color:#c0c0ff;margin-bottom:1.5rem;">{% if host %}Edit Host{% else %}Add Host{% endif %}</h1>
+    <h1 class="page-title">{% if host %}Edit Host{% else %}Add Host{% endif %}</h1>
     <div class="card">
         <form method="post" action="{% if host %}/hosts/{{ host.id }}{% else %}/hosts/{% endif %}">
             <div class="form-group">
@@ -15,7 +15,7 @@
             </div>
             <div class="form-group">
                 <label>Probe Type</label>
-                <select name="probe_type" style="width:100%;padding:0.5rem 0.75rem;background:#0f0f1e;border:1px solid #3a3a5a;border-radius:4px;color:#e0e0e0;">
+                <select name="probe_type">
                     {% for pt in probe_types %}
                     <option value="{{ pt.value }}" {% if host and host.probe_type == pt %}selected{% endif %}>
                         {{ pt.value | upper }}
@@ -44,8 +44,8 @@
                 <input type="text" name="dns_expected_ip" value="{{ host.dns_expected_ip if host and host.dns_expected_ip else '' }}">
             </div>
             <div style="display:flex;gap:1rem;margin-top:1.5rem;">
-                <button type="submit">{% if host %}Save{% else %}Add Host{% endif %}</button>
-                <a href="/hosts/" style="padding:0.5rem 1rem;color:#a0a0c0;text-decoration:none;">Cancel</a>
+                <button type="submit" class="btn">{% if host %}Save{% else %}Add Host{% endif %}</button>
+                <a href="/hosts/" class="btn btn-ghost">Cancel</a>
             </div>
         </form>
     </div>