Select usable Flanders theme by default

backend/tests/test_sprint237_flanders_thematic_on_demand.py

@@ -17,6 +17,8 @@ def test_flanders_workspace_exposes_governed_thematic_products_on_demand() -> No
     assert "activeScopeProject?.name === FLANDERS_WORKSPACE_PROJECT_NAME" in workspace
     assert "new Map<DataThemeId, ThematicRasterProductRead>" in workspace
     assert "'Op aanvraag'" in workspace
+    assert "theme.id === 'space_occupation'" in workspace
+    assert "setActiveThemeId(fallbackTheme.id)" in workspace
     assert "thematicProductKey: thematicProduct.key" in workspace
     assert "datasetsApi.listThematicRasterProducts" in product_hook
     assert "datasetsApi.acquireThematicRaster" in selection_hook