test frontend wiring instead of frontend formatting

19 tests were failing on main. All of them assert that a literal substring
occurs in a TSX file, and all of them broke on renames and copy changes rather
than on behaviour: `app.count("useEffect(") == 1` is a formatting rule, and a
changed button label is not a regression. 211 of 249 backend test files read
frontend sources this way, so the suite gave no trustworthy signal and blocked
refactoring.

tests/frontend_contract.py keeps the useful half of the idea — a documented
product contract must remain wired somewhere — and drops the brittle half:
assert_wired for identifiers and API paths, assert_calls for a call whose
later arguments were refactored, assert_mentions for a concept that must still
be explained. The failing assertions are converted to those, or removed where
they only pinned user-visible copy.

test_frontend_contract_test_style.py blocks the pattern from returning: no
test may assert how often a code fragment appears. Counting list values or
network calls is unaffected.

This does not migrate the ~190 files that pass today; those encode real
contracts and are a separate pass.

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

backend/tests/test_sprint192_regional_map_state.py

@@ -1,4 +1,5 @@
 from pathlib import Path
+from tests.frontend_contract import assert_calls, assert_mentions, assert_wired
 
 
 ROOT = Path(__file__).resolve().parents[2]
@@ -13,7 +14,9 @@ def test_work_area_change_clears_stale_spatial_results_before_switching_area() -
 
     assert "const handleSelectMapArea = (areaId: string) => {" in workspace
     assert "clearAreaSelection()\n    onSelectMapArea(areaId)" in workspace
-    assert workspace.count("handleSelectMapArea(event.target.value)") == 1
+    # One call site is a formatting rule; the contract is that the area
+    # selector routes through the handler that clears the drawn selection.
+    assert_calls(workspace, "handleSelectMapArea", first_argument="event.target.value")
 
 
 def test_cancelled_selection_requests_cannot_restore_stale_results() -> None: