feat(canvas): Studio Enhancement Phase 1 & 2 - v2.0 architecture and file structure

Phase 1 - Foundation:
- Add NodeConfigPanelV2 using useSpecStore for AtomizerSpec v2.0 mode
- Deprecate AtomizerCanvas and useCanvasStore with migration docs
- Add VITE_USE_LEGACY_CANVAS env var for emergency fallback
- Enhance NodePalette with collapse support, filtering, exports
- Add drag-drop support to SpecRenderer with default node data
- Setup test infrastructure (Vitest + Playwright configs)
- Add useSpecStore unit tests (15 tests)

Phase 2 - File Structure & Model:
- Create FileStructurePanel with tree view of study files
- Add ModelNodeV2 with collapsible file dependencies
- Add tabbed left sidebar (Components/Files tabs)
- Add GET /api/files/structure/{study_id} backend endpoint
- Auto-expand 1_setup folders in file tree
- Show model file introspection with solver type and expressions

Technical:
- All TypeScript checks pass
- All 15 unit tests pass
- Production build successful

atomizer-dashboard/frontend/src/test/setup.ts

@@ -0,0 +1,137 @@
+/**
+ * Vitest Test Setup
+ * 
+ * This file runs before each test file to set up the testing environment.
+ */
+
+/// <reference types="vitest/globals" />
+
+import '@testing-library/jest-dom';
+import { vi, beforeAll, afterAll, afterEach } from 'vitest';
+
+// Type for global context
+declare const global: typeof globalThis;
+
+// ============================================================================
+// Mock Browser APIs
+// ============================================================================
+
+// Mock ResizeObserver (used by ReactFlow)
+global.ResizeObserver = vi.fn().mockImplementation(() => ({
+  observe: vi.fn(),
+  unobserve: vi.fn(),
+  disconnect: vi.fn(),
+}));
+
+// Mock IntersectionObserver
+global.IntersectionObserver = vi.fn().mockImplementation(() => ({
+  observe: vi.fn(),
+  unobserve: vi.fn(),
+  disconnect: vi.fn(),
+}));
+
+// Mock matchMedia
+Object.defineProperty(window, 'matchMedia', {
+  writable: true,
+  value: vi.fn().mockImplementation((query: string) => ({
+    matches: false,
+    media: query,
+    onchange: null,
+    addListener: vi.fn(),
+    removeListener: vi.fn(),
+    addEventListener: vi.fn(),
+    removeEventListener: vi.fn(),
+    dispatchEvent: vi.fn(),
+  })),
+});
+
+// Mock scrollTo
+Element.prototype.scrollTo = vi.fn();
+window.scrollTo = vi.fn();
+
+// Mock fetch for API calls
+global.fetch = vi.fn();
+
+// ============================================================================
+// Mock localStorage
+// ============================================================================
+
+const localStorageMock = {
+  getItem: vi.fn(),
+  setItem: vi.fn(),
+  removeItem: vi.fn(),
+  clear: vi.fn(),
+  length: 0,
+  key: vi.fn(),
+};
+Object.defineProperty(window, 'localStorage', { value: localStorageMock });
+
+// ============================================================================
+// Mock WebSocket
+// ============================================================================
+
+class MockWebSocket {
+  static readonly CONNECTING = 0;
+  static readonly OPEN = 1;
+  static readonly CLOSING = 2;
+  static readonly CLOSED = 3;
+
+  readonly CONNECTING = 0;
+  readonly OPEN = 1;
+  readonly CLOSING = 2;
+  readonly CLOSED = 3;
+
+  url: string;
+  readyState: number = MockWebSocket.CONNECTING;
+  onopen: ((event: Event) => void) | null = null;
+  onclose: ((event: CloseEvent) => void) | null = null;
+  onmessage: ((event: MessageEvent) => void) | null = null;
+  onerror: ((event: Event) => void) | null = null;
+
+  constructor(url: string) {
+    this.url = url;
+    // Simulate connection after a tick
+    setTimeout(() => {
+      this.readyState = MockWebSocket.OPEN;
+      this.onopen?.(new Event('open'));
+    }, 0);
+  }
+
+  send = vi.fn();
+  close = vi.fn(() => {
+    this.readyState = MockWebSocket.CLOSED;
+    this.onclose?.(new CloseEvent('close'));
+  });
+}
+
+global.WebSocket = MockWebSocket as any;
+
+// ============================================================================
+// Console Suppression (optional)
+// ============================================================================
+
+// Suppress console.error for expected test warnings
+const originalError = console.error;
+beforeAll(() => {
+  console.error = (...args: any[]) => {
+    // Suppress React act() warnings
+    if (typeof args[0] === 'string' && args[0].includes('Warning: An update to')) {
+      return;
+    }
+    originalError.call(console, ...args);
+  };
+});
+
+afterAll(() => {
+  console.error = originalError;
+});
+
+// ============================================================================
+// Cleanup
+// ============================================================================
+
+afterEach(() => {
+  vi.clearAllMocks();
+  localStorageMock.getItem.mockReset();
+  localStorageMock.setItem.mockReset();
+});