perf(map): analyze only the selected theme

backend/tests/test_sprint237_flanders_thematic_on_demand.py

@@ -34,7 +34,8 @@ def test_selection_reads_and_bounded_acquires_all_relevant_themes() -> None:
     app = read("frontend/src/App.tsx")
     selection_hook = read("frontend/src/hooks/useMapThemeSelectionInsights.ts")
 
-    assert "for (const theme of DATA_THEMES)" in workspace
+    assert "for (const theme of [activeTheme])" in workspace
+    assert "loadSelectedThemeResult" in workspace
     assert "? onDemandProductsForZones(resolvedZones)" in workspace
     assert ".filter((product) => product.theme === activeThemeId)" not in workspace
     assert "await loadThemeInsights(bbox, availableThemes, areaId)" in workspace