Redesign frontend with clean light theme and design system

Replace prototype dark theme with a professional light-theme design
using Outfit (UI) and IBM Plex Mono (data) fonts, navy topbar, white
card surfaces, and a full CSS variable system for colors, shadows,
spacing, and radii. Add LED status indicators, panel components,
and structured tile layout with header/meta/footer sections.

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

internal/web/static/app.js

@@ -5,13 +5,13 @@
   function connect() {
     es = new EventSource('/events');
     es.addEventListener('hello', function() {
-      dot.classList.remove('disconnected');
+      dot.className = 'led led-green';
     });
     es.addEventListener('host.state_changed', function() {
       window.location.reload();
     });
     es.onerror = function() {
-      dot.classList.add('disconnected');
+      dot.className = 'led led-red';
       es.close();
       setTimeout(connect, 3000);
     };