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/tests/integration/test_api_health.py

@@ -0,0 +1,25 @@
+"""Basic API smoke tests."""
+import pytest
+
+
+@pytest.mark.asyncio
+async def test_health_endpoint(client):
+    resp = await client.get("/health")
+    assert resp.status_code == 200
+
+
+@pytest.mark.asyncio
+async def test_settings_requires_auth(client):
+    """Settings endpoint ohne Auth → 401/403."""
+    resp = await client.get("/api/admin/settings")
+    assert resp.status_code in (401, 403)
+
+
+@pytest.mark.asyncio
+async def test_admin_settings_with_auth(client, auth_headers):
+    """Settings endpoint mit Admin-Token → 200."""
+    resp = await client.get("/api/admin/settings", headers=auth_headers)
+    assert resp.status_code == 200
+    data = resp.json()
+    assert "blender_engine" in data
+    assert "thumbnail_format" in data