feat: implement v0.4.0 - Reports, Charts, Comparison, Dark Mode, E2E Testing

Backend (@backend-dev):
- Add ReportService with PDF/CSV generation (reportlab, pandas)
- Implement Report API endpoints (POST, GET, DELETE, download)
- Add ReportRepository and schemas
- Configure storage with auto-cleanup (30 days)
- Rate limiting: 10 downloads/minute
- Professional PDF templates with charts support

Frontend (@frontend-dev):
- Integrate Recharts for data visualization
- Add CostBreakdown, TimeSeries, ComparisonBar charts
- Implement scenario comparison page with multi-select
- Add dark/light mode toggle with ThemeProvider
- Create Reports page with generation form and list
- Add new UI components: checkbox, dialog, tabs, label, skeleton
- Implement useComparison and useReports hooks

QA (@qa-engineer):
- Setup Playwright E2E testing framework
- Create 7 test spec files with 94 test cases
- Add visual regression testing with baselines
- Configure multi-browser testing (Chrome, Firefox, WebKit)
- Add mobile responsive tests
- Create test fixtures and helpers
- Setup GitHub Actions CI workflow

Documentation (@spec-architect):
- Create detailed kanban-v0.4.0.md with 27 tasks
- Update progress.md with v0.4.0 tracking
- Create v0.4.0 planning prompt

Features:
✅ PDF/CSV Report Generation
✅ Interactive Charts (Pie, Area, Bar)
✅ Scenario Comparison (2-4 scenarios)
✅ Dark/Light Mode Toggle
✅ E2E Test Suite (94 tests)

Dependencies added:
- Backend: reportlab, pandas, slowapi
- Frontend: recharts, date-fns, @radix-ui/react-checkbox/dialog/tabs
- Testing: @playwright/test

27 tasks completed, 100% v0.4.0 implementation

frontend/playwright.config.ts

@@ -0,0 +1,112 @@
+import { defineConfig, devices } from '@playwright/test';
+import path from 'path';
+
+/**
+ * Playwright configuration for mockupAWS E2E testing
+ * @see https://playwright.dev/docs/test-configuration
+ */
+export default defineConfig({
+  // Test directory
+  testDir: './e2e',
+
+  // Run tests in files in parallel
+  fullyParallel: true,
+
+  // Fail the build on CI if you accidentally left test.only in the source code
+  forbidOnly: !!process.env.CI,
+
+  // Retry on CI only
+  retries: process.env.CI ? 2 : 0,
+
+  // Opt out of parallel tests on CI for stability
+  workers: process.env.CI ? 1 : undefined,
+
+  // Reporter to use
+  reporter: [
+    ['html', { outputFolder: 'e2e-report' }],
+    ['list'],
+    ['junit', { outputFile: 'e2e-report/results.xml' }],
+  ],
+
+  // Shared settings for all the projects below
+  use: {
+    // Base URL to use in actions like `await page.goto('/')`
+    baseURL: 'http://localhost:5173',
+
+    // Collect trace when retrying the failed test
+    trace: 'on-first-retry',
+
+    // Capture screenshot on failure
+    screenshot: 'only-on-failure',
+
+    // Record video for debugging
+    video: 'on-first-retry',
+
+    // Action timeout
+    actionTimeout: 15000,
+
+    // Navigation timeout
+    navigationTimeout: 30000,
+
+    // Viewport size
+    viewport: { width: 1280, height: 720 },
+  },
+
+  // Configure projects for major browsers
+  projects: [
+    {
+      name: 'chromium',
+      use: { ...devices['Desktop Chrome'] },
+    },
+
+    {
+      name: 'firefox',
+      use: { ...devices['Desktop Firefox'] },
+    },
+
+    {
+      name: 'webkit',
+      use: { ...devices['Desktop Safari'] },
+    },
+
+    // Mobile viewports
+    {
+      name: 'Mobile Chrome',
+      use: { ...devices['Pixel 5'] },
+    },
+
+    {
+      name: 'Mobile Safari',
+      use: { ...devices['iPhone 12'] },
+    },
+
+    // Tablet viewport
+    {
+      name: 'Tablet',
+      use: { ...devices['iPad Pro 11'] },
+    },
+  ],
+
+  // Run local dev server before starting the tests
+  webServer: {
+    command: 'npm run dev',
+    url: 'http://localhost:5173',
+    reuseExistingServer: !process.env.CI,
+    timeout: 120 * 1000,
+  },
+
+  // Output directory for test artifacts
+  outputDir: path.join(__dirname, 'e2e-results'),
+
+  // Timeout for each test
+  timeout: 60000,
+
+  // Expect timeout for assertions
+  expect: {
+    timeout: 10000,
+  },
+
+  // Global setup and teardown
+  globalSetup: require.resolve('./e2e/global-setup.ts'),
+  globalTeardown: require.resolve('./e2e/global-teardown.ts'),
+});