feat(canvas): Canvas V3 - Bug fixes and study workflow improvements

Bug Fixes:
- Fix Atomizer Assistant error with reconnect button and error state handling
- Enable connection/edge deletion with keyboard Delete/Backspace keys
- Fix drag & drop positioning using screenToFlowPosition correctly
- Fix loadFromConfig to create all node types and edges properly

UI/UX Improvements:
- Minimal responsive header with context breadcrumb
- Better contrast with white text on dark backgrounds
- Larger font sizes in NodePalette for readability
- Study-aware header showing selected study name

New Features:
- Enhanced ExecuteDialog with Create/Update mode toggle
- Select existing study to update or create new study
- Home page Canvas Builder button for quick access
- Home navigation button in CanvasView header

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

atomizer-dashboard/frontend/src/components/canvas/palette/NodePalette.tsx

@@ -37,31 +37,31 @@ export function NodePalette() {
   };
 
   return (
-    <div className="w-56 bg-dark-850 border-r border-dark-700 flex flex-col">
+    <div className="w-60 bg-dark-850 border-r border-dark-700 flex flex-col">
       <div className="p-4 border-b border-dark-700">
-        <h3 className="text-xs font-semibold text-dark-400 uppercase tracking-wider">
+        <h3 className="text-sm font-semibold text-dark-300 uppercase tracking-wider">
           Components
         </h3>
-        <p className="text-xs text-dark-500 mt-1">
+        <p className="text-xs text-dark-400 mt-1">
           Drag to canvas
         </p>
       </div>
-      <div className="flex-1 overflow-y-auto p-3 space-y-1.5">
+      <div className="flex-1 overflow-y-auto p-3 space-y-2">
         {PALETTE_ITEMS.map((item) => (
           <div
             key={item.type}
             draggable
             onDragStart={(e) => onDragStart(e, item.type)}
-            className="flex items-center gap-2.5 px-3 py-2.5 bg-dark-800/50 rounded-lg border border-dark-700/50
+            className="flex items-center gap-3 px-3 py-3 bg-dark-800/50 rounded-lg border border-dark-700/50
                        cursor-grab hover:border-primary-500/50 hover:bg-dark-800
                        active:cursor-grabbing transition-all group"
           >
-            <div className={`${item.color} opacity-80 group-hover:opacity-100 transition-opacity`}>
+            <div className={`${item.color} opacity-90 group-hover:opacity-100 transition-opacity`}>
               {item.icon}
             </div>
             <div className="flex-1 min-w-0">
-              <div className="font-medium text-dark-200 text-sm leading-tight">{item.label}</div>
-              <div className="text-[10px] text-dark-500 truncate">{item.description}</div>
+              <div className="font-semibold text-white text-sm leading-tight">{item.label}</div>
+              <div className="text-xs text-dark-400 truncate">{item.description}</div>
             </div>
           </div>
         ))}