feat: Phase 1 - Canvas with React Flow

- 8 node types (Model, Solver, DesignVar, Extractor, Objective, Constraint, Algorithm, Surrogate)
- Drag-drop from palette to canvas
- Node configuration panels
- Graph validation with error/warning display
- Intent JSON serialization
- Zustand state management

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

atomizer-dashboard/frontend/package.json

@@ -31,13 +31,15 @@
     "react-router-dom": "^6.20.0",
     "react-syntax-highlighter": "^16.1.0",
     "react-use-websocket": "^4.13.0",
+    "reactflow": "^11.11.4",
     "recharts": "^2.10.3",
     "rehype-katex": "^7.0.1",
     "remark-gfm": "^4.0.1",
     "remark-math": "^6.0.0",
     "tailwind-merge": "^3.4.0",
     "three": "^0.181.2",
-    "xterm": "^5.3.0"
+    "xterm": "^5.3.0",
+    "zustand": "^5.0.10"
   },
   "devDependencies": {
     "@types/react": "^18.2.43",