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/frontend_contract.py

@@ -32,6 +32,7 @@ MAP_WORKSPACE_SOURCES = (
     "components/map/mapWorkspaceUtils.ts",
     "hooks/useMapImageOverlays.ts",
     "hooks/useMapRectangleSelection.ts",
+    "hooks/useFullGisWorkflow.ts",
     "components/map/MapExplorerView.tsx",
     "components/map/MapAdvancedWorkbench.tsx",
 )