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/pages/Home.tsx

@@ -17,7 +17,8 @@ import {
   Folder,
   FolderOpen,
   Maximize2,
-  X
+  X,
+  Layers
 } from 'lucide-react';
 import { useStudy } from '../context/StudyContext';
 import { Study } from '../types';
@@ -172,19 +173,33 @@ const Home: React.FC = () => {
                 className="h-10 md:h-12"
               />
             </div>
-            <button
-              onClick={() => refreshStudies()}
-              disabled={isLoading}
-              className="flex items-center gap-2 px-4 py-2 rounded-lg transition-all disabled:opacity-50 hover:border-primary-400/40"
-              style={{
-                background: 'rgba(8, 15, 26, 0.85)',
-                border: '1px solid rgba(0, 212, 230, 0.2)',
-                color: '#fff'
-              }}
-            >
-              <RefreshCw className={`w-4 h-4 text-primary-400 ${isLoading ? 'animate-spin' : ''}`} />
-              Refresh
-            </button>
+            <div className="flex items-center gap-3">
+              <button
+                onClick={() => navigate('/canvas')}
+                className="flex items-center gap-2 px-4 py-2 rounded-lg transition-all font-medium hover:-translate-y-0.5"
+                style={{
+                  background: 'linear-gradient(135deg, #00d4e6 0%, #0891b2 100%)',
+                  color: '#000',
+                  boxShadow: '0 4px 15px rgba(0, 212, 230, 0.3)'
+                }}
+              >
+                <Layers className="w-4 h-4" />
+                Canvas Builder
+              </button>
+              <button
+                onClick={() => refreshStudies()}
+                disabled={isLoading}
+                className="flex items-center gap-2 px-4 py-2 rounded-lg transition-all disabled:opacity-50 hover:border-primary-400/40"
+                style={{
+                  background: 'rgba(8, 15, 26, 0.85)',
+                  border: '1px solid rgba(0, 212, 230, 0.2)',
+                  color: '#fff'
+                }}
+              >
+                <RefreshCw className={`w-4 h-4 text-primary-400 ${isLoading ? 'animate-spin' : ''}`} />
+                Refresh
+              </button>
+            </div>
           </div>
         </div>
       </header>