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>

backend/app/main.py

@@ -23,6 +23,7 @@ from app.domains.tenants.router import router as tenants_router
 from app.domains.rendering.workflow_router import router as workflows_router
 from app.domains.media.router import router as media_router
 from app.api.routers.asset_libraries import router as asset_libraries_router
+from app.domains.admin.dashboard_router import router as dashboard_router
 
 
 @asynccontextmanager
@@ -88,6 +89,7 @@ app.include_router(tenants_router, prefix="/api")
 app.include_router(workflows_router)
 app.include_router(media_router)
 app.include_router(asset_libraries_router, prefix="/api")
+app.include_router(dashboard_router, prefix="/api")
 
 
 @app.get("/health")