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

src/api/v1/__init__.py

@@ -5,8 +5,13 @@ from fastapi import APIRouter
 from src.api.v1.scenarios import router as scenarios_router
 from src.api.v1.ingest import router as ingest_router
 from src.api.v1.metrics import router as metrics_router
+from src.api.v1.reports import scenario_reports_router, reports_router
 
 api_router = APIRouter()
 api_router.include_router(scenarios_router, prefix="/scenarios", tags=["scenarios"])
 api_router.include_router(ingest_router, tags=["ingest"])
 api_router.include_router(metrics_router, prefix="/scenarios", tags=["metrics"])
+api_router.include_router(
+    scenario_reports_router, prefix="/scenarios", tags=["reports"]
+)
+api_router.include_router(reports_router, prefix="/reports", tags=["reports"])