feat(L+M): configurable dashboard widget system + test framework

Phase L: Dashboard widget system
- Migration 046: dashboard_configs table (user/tenant/role fallback cascade)
- DashboardConfig model + dashboard_service with get/upsert per-user and tenant-default
- API router: GET/PUT /api/dashboard/config, GET/PUT /api/dashboard/tenant-default
- Frontend: 5 widget components (ProductionStats, QueueStatus, RecentRenders, CostOverview, WorkerStatus)
- DashboardGrid with API-backed config, DashboardCustomizeModal (checkbox selection, save/cancel)
- Dashboard.tsx: widget grid + analytics section (privileged users)
- Admin.tsx: restructured with new section order and Maintenance 2-col grid

Phase M: Test framework
- Backend: pytest-asyncio + pytest-cov + factory-boy in pyproject.toml
- conftest.py: excel_dir fixtures + async DB fixtures + mock storage/celery stubs
- Domain tests: billing_service, cache_service, notifications_service, imports_sanity
- Integration: test_api_health.py smoke test (requires running backend)
- Frontend: vitest + @testing-library/react + msw added to package.json
- vite.config.ts: test block (jsdom + globals + setupFiles)
- tsconfig.json: exclude src/__tests__ from main tsc (test runner handles its own types)
- MSW handlers for /api/auth/me, Billing.test.tsx, formatters.test.ts

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/__tests__/utils/formatters.test.ts

@@ -0,0 +1,16 @@
+import { describe, test, expect } from 'vitest'
+
+// Teste pure utility-Funktionen
+describe('Formatter utilities', () => {
+  test('EUR formatting', () => {
+    const amount = 1234.56
+    const formatted = new Intl.NumberFormat('de-DE', { style: 'currency', currency: 'EUR' }).format(amount)
+    expect(formatted).toContain('1.234,56')
+  })
+
+  test('date formatting', () => {
+    const d = new Date('2026-03-06T00:00:00Z')
+    const iso = d.toISOString().slice(0, 10)
+    expect(iso).toBe('2026-03-06')
+  })
+})