test(fix): stop handover widget test hanging on awaited stream .first

The 'giving all with payment and promise' widget test awaited
repo.watchSales().first / watchPlantares().first in its body. A Drift
stream's .first never completes under the widget-test fake-async clock
(pumpAndSettle has already returned, so dart_test.yaml's per-test timeout
can't bound it), so the test hung to the framework's 10-min hard cap.

- Read the recorded sale/plantare with one-shot db.select(...).get()
  queries instead (same filter, resolves fine under fake-async) — the
  suite now passes in ~1s.
- Add a pure-Dart guard test that scans test/ui/ and fails loudly if any
  awaited watchX().first reappears, so this stops being recurrent.

apps/app_seeds/test/ui/handover_sheet_test.dart

@@ -84,13 +84,21 @@ void main() {
     await tester.tap(find.byKey(const Key('handover.save')));
     await tester.pumpAndSettle();
 
-    final sales = await repo.watchSales().first;
+    // One-shot .get() reads (NOT watch().first): a Drift stream's `.first`
+    // never completes under the widget-test fake-async clock, so awaiting it
+    // in a testWidgets body hangs the whole test to the 10-min hard cap. A
+    // plain SELECT resolves fine (same as the movements/lot reads below).
+    final sales = await (db.select(
+      db.sales,
+    )..where((s) => s.isDeleted.equals(false))).get();
     expect(sales.single.direction, SaleDirection.iSold);
     expect(sales.single.amount, 2.5);
     expect(sales.single.currency, 'Ğ1');
     expect(sales.single.counterparty, 'María');
 
-    final plantares = await repo.watchPlantares().first;
+    final plantares = await (db.select(
+      db.plantares,
+    )..where((p) => p.isDeleted.equals(false))).get();
     expect(plantares.single.direction, PlantareDirection.owedToMe);
     expect(plantares.single.owedDescription, 'un puñado');