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/src/components/canvas/nodes/index.ts

@@ -0,0 +1,30 @@
+import { ModelNode } from './ModelNode';
+import { SolverNode } from './SolverNode';
+import { DesignVarNode } from './DesignVarNode';
+import { ExtractorNode } from './ExtractorNode';
+import { ObjectiveNode } from './ObjectiveNode';
+import { ConstraintNode } from './ConstraintNode';
+import { AlgorithmNode } from './AlgorithmNode';
+import { SurrogateNode } from './SurrogateNode';
+
+export {
+  ModelNode,
+  SolverNode,
+  DesignVarNode,
+  ExtractorNode,
+  ObjectiveNode,
+  ConstraintNode,
+  AlgorithmNode,
+  SurrogateNode,
+};
+
+export const nodeTypes = {
+  model: ModelNode,
+  solver: SolverNode,
+  designVar: DesignVarNode,
+  extractor: ExtractorNode,
+  objective: ObjectiveNode,
+  constraint: ConstraintNode,
+  algorithm: AlgorithmNode,
+  surrogate: SurrogateNode,
+};