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/index.html

@@ -0,0 +1,16 @@
+{% extends "base.html" %}
+{% block title %}DNS Monitor — FabledNetMon{% endblock %}
+{% block content %}
+<div style="display:flex;align-items:center;justify-content:space-between;margin-bottom:1.5rem;">
+  <h1 class="page-title" style="margin-bottom:0;">DNS Monitor</h1>
+  <span style="color:var(--text-muted);font-size:0.85rem;">polling every {{ poll_interval }}s</span>
+</div>
+<div class="card ping-card">
+  <div id="dns-rows"
+       hx-get="/dns/rows"
+       hx-trigger="every {{ poll_interval }}s"
+       hx-swap="innerHTML">
+    {% include "dns/rows.html" %}
+  </div>
+</div>
+{% endblock %}