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_sprint198_detection_review_completion.py

@@ -4,6 +4,7 @@ import importlib.util
 from pathlib import Path
 
 import pytest
+from tests.frontend_contract import read_map_workspace
 
 
 ROOT = Path(__file__).resolve().parents[2]
@@ -118,9 +119,7 @@ def test_readiness_compiles_false_negative_review_validator() -> None:
 
 
 def test_map_explains_strict_and_diagnostic_detection_matching() -> None:
-    workspace = (
-        ROOT / "frontend" / "src" / "components" / "map" / "MapWorkspace.tsx"
-    ).read_text(encoding="utf-8")
+    workspace = read_map_workspace()
     # Both matching methods must be named; the exact label may change.
     assert "strikte" in workspace.casefold()
     assert "Rechthoekcontrole" in workspace