extract the map workspace's domain layer out of the component

MapWorkspace.tsx opened with ~590 lines of theme catalogue, dataset matching
and label formatting above a 3.200-line component. None of it is React, all of
it is independently testable, and both render paths read from it, so it belongs
beside the pure helpers that already live in mapWorkspaceUtils.

The contract tests that read MapWorkspace.tsx would have gone red for a move
that changes no behaviour at all — 24 of them. That is the brittleness the
frontend_contract helper exists to remove, so it gains read_map_workspace():
the workspace is one feature spread over several modules, and a contract
belongs to the feature rather than to whichever file currently holds it.

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

backend/tests/test_rc4_national_coverage.py

@@ -13,6 +13,7 @@ from app.models import Area, Dataset, Project
 from app.schemas.coverage import CoverageBBox
 from app.services.coverage_registry_service import CoverageRegistryService, THEMES, ZONES
 from app.services.vector_feature_service import VectorFeatureService
+from tests.frontend_contract import read_map_workspace
 
 
 class FakeQuery:
@@ -151,9 +152,7 @@ def test_national_and_maritime_reference_layers_are_selection_analyzable() -> No
 def test_national_scope_operator_assigns_explicit_map_themes() -> None:
     root = Path(__file__).resolve().parents[2]
     operator = (root / "scripts" / "provision_belgium_north_sea_scope.py").read_text(encoding="utf-8")
-    map_workspace = (root / "frontend" / "src" / "components" / "map" / "MapWorkspace.tsx").read_text(
-        encoding="utf-8"
-    )
+    map_workspace = read_map_workspace()
 
     assert '"belgium_municipalities": "administrative"' in operator
     assert '"marine_legal_scopes": "marine_environment"' in operator
@@ -476,7 +475,7 @@ def test_frontend_prefers_materialized_national_workspace_and_resolves_drawn_bbo
     focus = (root / "frontend" / "src" / "config" / "primaryFocus.ts").read_text(encoding="utf-8")
     workspace_hook = (root / "frontend" / "src" / "hooks" / "useProjectWorkspace.ts").read_text(encoding="utf-8")
     coverage_hook = (root / "frontend" / "src" / "hooks" / "useCoverageResolver.ts").read_text(encoding="utf-8")
-    map_workspace = (root / "frontend" / "src" / "components" / "map" / "MapWorkspace.tsx").read_text(encoding="utf-8")
+    map_workspace = read_map_workspace()
 
     assert "Belgium and North Sea Workbench" in focus
     assert "nationalProject" in workspace_hook