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/e2e/global-teardown.ts

@@ -0,0 +1,55 @@
+/**
+ * Global Teardown for Playwright E2E Tests
+ * 
+ * This runs once after all test suites complete.
+ * Used for:
+ * - Database cleanup
+ * - Test artifact archival
+ * - Environment reset
+ */
+
+import { execSync } from 'child_process';
+import path from 'path';
+import fs from 'fs';
+
+async function globalTeardown() {
+  console.log('🧹 Starting E2E test teardown...');
+
+  const testStartTime = process.env.TEST_START_TIME;
+  console.log(`   Test started at: ${testStartTime}`);
+  console.log(`   Test completed at: ${new Date().toISOString()}`);
+
+  // Clean up temporary test files if in CI mode
+  if (process.env.CI) {
+    console.log('   CI mode: Cleaning up temporary files...');
+    const resultsDir = path.join(__dirname, '..', 'e2e-results');
+    
+    // Keep videos/screenshots of failures for debugging
+    // but clean up successful test artifacts after 7 days
+    if (fs.existsSync(resultsDir)) {
+      const files = fs.readdirSync(resultsDir);
+      let cleanedCount = 0;
+      
+      for (const file of files) {
+        const filePath = path.join(resultsDir, file);
+        const stats = fs.statSync(filePath);
+        const ageInDays = (Date.now() - stats.mtime.getTime()) / (1000 * 60 * 60 * 24);
+        
+        if (ageInDays > 7 && !file.includes('failed')) {
+          try {
+            fs.unlinkSync(filePath);
+            cleanedCount++;
+          } catch (e) {
+            // Ignore errors during cleanup
+          }
+        }
+      }
+      
+      console.log(`   Cleaned up ${cleanedCount} old test artifacts`);
+    }
+  }
+
+  console.log('✅ E2E test teardown complete');
+}
+
+export default globalTeardown;