feat: complete v0.4.0 implementation - Reports, Charts, Comparison, Dark Mode

Backend (@backend-dev):
- ReportService with PDF/CSV generation (reportlab, pandas)
- Report API endpoints (POST, GET, DELETE, download with rate limiting)
- Professional PDF templates with branding and tables
- Storage management with auto-cleanup

Frontend (@frontend-dev):
- Recharts integration: CostBreakdown, TimeSeries, ComparisonBar
- Scenario comparison: multi-select, compare page with side-by-side layout
- Reports UI: generation form, list with status badges, download
- Dark/Light mode: ThemeProvider, toggle, CSS variables
- Responsive design for all components

QA (@qa-engineer):
- E2E testing setup with Playwright
- 100 test cases across 7 spec files
- Visual regression baselines
- CI/CD workflow configuration
- ES modules fixes

Documentation:
- Add todo.md with testing checklist and future roadmap
- Update kickoff prompt for v0.4.0

27 tasks completed, 100% v0.4.0 delivery

Closes: v0.4.0 milestone

frontend/playwright.config.ts

@@ -31,7 +31,7 @@ export default defineConfig({
   // Shared settings for all the projects below
   use: {
     // Base URL to use in actions like `await page.goto('/')`
-    baseURL: 'http://localhost:5173',
+    baseURL: process.env.TEST_BASE_URL || 'http://localhost:5173',
 
     // Collect trace when retrying the failed test
     trace: 'on-first-retry',
@@ -93,6 +93,8 @@ export default defineConfig({
     url: 'http://localhost:5173',
     reuseExistingServer: !process.env.CI,
     timeout: 120 * 1000,
+    stdout: 'pipe',
+    stderr: 'pipe',
   },
 
   // Output directory for test artifacts