style(design): migrate to DESIGN.md system

Full visual migration: Space Grotesk + DM Sans + JetBrains Mono fonts,
warm amber two-accent system (amber=state, blue=action), dark mode with
CSS vars + localStorage + FOUC prevention, mobile bottom nav (5 tabs),
full-width tables, error/skipped dot glow, ~13 hardcoded hex replaced
with CSS vars in 4 JS files, 5 new E2E tests.

Files: style.css (full rewrite), base.html (fonts, theme script, dark
toggle, bottom nav), settings.html (dark toggle card), dashboard.js,
logs.js, mappings.js, settings.js (color vars), 5 templates (bnav
active blocks), test_design_system_e2e.py (NEW).

Cache-bust: style.css?v=18, shared.js?v=14, dashboard.js?v=27,
logs.js?v=13, mappings.js?v=12, settings.js?v=8

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/app/templates/settings.html

@@ -1,10 +1,23 @@
 {% extends "base.html" %}
 {% block title %}Setari - GoMag Import{% endblock %}
 {% block nav_settings %}active{% endblock %}
+{% block bnav_settings %}active{% endblock %}
+{% block main_class %}constrained{% endblock %}
 
 {% block content %}
 <h4 class="mb-3">Setari</h4>
 
+<!-- Dark mode toggle -->
+<div class="theme-toggle-card">
+    <div>
+        <i class="bi bi-moon-fill me-2"></i>
+        <label for="settDarkMode">Mod intunecat</label>
+    </div>
+    <div class="form-check form-switch mb-0">
+        <input class="form-check-input" type="checkbox" role="switch" id="settDarkMode" style="width:2.5rem;height:1.25rem">
+    </div>
+</div>
+
 <div class="row g-3 mb-3">
     <!-- GoMag API card -->
     <div class="col-md-6">
@@ -233,5 +246,5 @@
 {% endblock %}
 
 {% block scripts %}
-<script src="{{ request.scope.get('root_path', '') }}/static/js/settings.js?v=7"></script>
+<script src="{{ request.scope.get('root_path', '') }}/static/js/settings.js?v=8"></script>
 {% endblock %}