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/models/__init__.py

@@ -13,6 +13,7 @@ from app.domains.billing.models import PricingTier
 from app.domains.rendering.models import OutputType, RenderTemplate, ProductRenderPosition, WorkflowDefinition, WorkflowRun, WorkflowNodeResult
 from app.domains.materials.models import Material, MaterialAlias, AssetLibrary
 from app.domains.media.models import MediaAsset, MediaAssetType
+from app.domains.admin.models import DashboardConfig
 
 # Also re-export SystemSetting (no domain assigned — stays as-is)
 from app.models.system_setting import SystemSetting
@@ -22,4 +23,5 @@ __all__ = [
     "AuditLog", "PricingTier", "OutputType", "RenderTemplate", "ProductRenderPosition",
     "WorkflowDefinition", "WorkflowRun", "WorkflowNodeResult",
     "Material", "MaterialAlias", "AssetLibrary", "MediaAsset", "MediaAssetType", "SystemSetting",
+    "DashboardConfig",
 ]