feat(canvas): Responsive full-screen layout and dark theme

Phase 2 of Canvas Professional Upgrade:
- Update AtomizerCanvas with Lucide icons (MessageCircle, Plug, X)
- Update CanvasView page with dark theme styling
- Replace emoji buttons with Lucide icons (ClipboardList, Download, Trash2)
- Update Setup canvas tab for full-width responsive layout
- Use calc(100vh-6rem) for proper canvas height

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

atomizer-dashboard/frontend/src/pages/Setup.tsx

@@ -254,12 +254,12 @@ export default function Setup() {
     return acc * 1000; // Approximate for continuous
   }, 1) || 0;
 
-  // Canvas tab - full height
+  // Canvas tab - full height and full width
   if (activeTab === 'canvas') {
     return (
-      <div className="w-full h-full flex flex-col">
+      <div className="w-full h-[calc(100vh-6rem)] flex flex-col -mx-6 -my-6 px-4 pt-4">
         {/* Tab Bar */}
-        <div className="flex items-center gap-2 mb-4 border-b border-dark-700 pb-4">
+        <div className="flex items-center gap-2 mb-3 border-b border-dark-700 pb-3">
           <button
             onClick={() => setActiveTab('config')}
             className="flex items-center gap-2 px-4 py-2 rounded-lg transition-colors bg-dark-800 text-dark-300 hover:text-white hover:bg-dark-700"