extract and test the four-step GIS workflow

Extracted for its error paths, not its size. Every step can fail or return
nothing, and each outcome has to leave the operator with a status that says
where the chain stopped — a workflow reporting "afgerond" after a step produced
nothing tells them a result exists when it does not. Inline in the component,
none of that was exercised; it now has fourteen tests covering each stopping
point, both rejection kinds, the reuse path and the preconditions.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/tests/test_sprint116_operational_gis_map_workflow.py

@@ -1,4 +1,5 @@
 from pathlib import Path
+from tests.frontend_contract import read_map_workspace
 
 
 REPO_ROOT = Path(__file__).resolve().parents[2]
@@ -19,7 +20,7 @@ def test_map_uses_road_basemap_with_attribution_and_env_override() -> None:
 
 
 def test_map_workspace_can_select_persisted_database_layer_and_run_query() -> None:
-    map_workspace = (REPO_ROOT / "frontend/src/components/map/MapWorkspace.tsx").read_text(encoding="utf-8")
+    map_workspace = read_map_workspace()
     app_shell = (REPO_ROOT / "frontend/src/App.tsx").read_text(encoding="utf-8")
     styles = (REPO_ROOT / "frontend/src/styles/app.css").read_text(encoding="utf-8")