feat(mvp): phase 7 - UI polish & ambient backgrounds

Add layout system (sidebar, header, main layout), dark/light/system theme
with HSL customization, 3 ambient backgrounds (mesh gradient, particle field,
aurora), Cmd/Ctrl+K search dialog, page transitions, card hover effects,
status pulse animations, skeleton loaders, and responsive design. Polish
all existing pages with consistent theming.

src/lib/components/app/AppHealthBadge.svelte

@@ -8,18 +8,18 @@
 	const config = $derived.by(() => {
 		switch (status) {
 			case 'online':
-				return { color: 'bg-green-500', text: 'Online' };
+				return { color: 'bg-green-500', cssClass: 'status-online', text: 'Online' };
 			case 'offline':
-				return { color: 'bg-red-500', text: 'Offline' };
+				return { color: 'bg-red-500', cssClass: '', text: 'Offline' };
 			case 'degraded':
-				return { color: 'bg-yellow-500', text: 'Degraded' };
+				return { color: 'bg-yellow-500', cssClass: '', text: 'Degraded' };
 			default:
-				return { color: 'bg-gray-500', text: 'Unknown' };
+				return { color: 'bg-gray-500', cssClass: '', text: 'Unknown' };
 		}
 	});
 </script>
 
 <span class="inline-flex items-center gap-1.5 text-xs">
-	<span class="inline-block h-2 w-2 rounded-full {config.color}"></span>
+	<span class="inline-block h-2 w-2 rounded-full {config.color} {config.cssClass}"></span>
 	<span class="text-muted-foreground">{config.text}</span>
 </span>