散布実績レビュー修正: バグ修正・仕様適合・デッドコード削除

- 候補API: 運搬済みフィルタ(date IS NOT NULL)を追加。
  delivery_plan_id指定時は全明細表示、年度全体時のみ日付フィルタ適用
- StockTransaction.spreading_item: CASCADE→SET_NULL に修正（仕様7.3準拠）
- perform_destroy: SET_NULL対応でUSEを明示削除してからsession削除
- ConfirmSpreadingModal.tsx: 未使用のため削除
- FertilizerEditPage.tsx: 旧散布確定関連デッドコード全除去
  (isConfirmed/confirmedAt state, handleUnconfirm, 確定取消ボタン, 確定済みバナー)
- services.py: 未使用のto_decimal_or_zero削除

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/apps/fertilizer/services.py

@@ -56,10 +56,3 @@ def sync_stock_uses_for_spreading_session(session):
             fertilization_plan=None,
             spreading_item=item,
         )
-
-
-def to_decimal_or_zero(value):
-    try:
-        return Decimal(str(value))
-    except Exception:
-        return Decimal('0')

backend/apps/fertilizer/views.py

@@ -381,8 +381,10 @@ class SpreadingSessionViewSet(viewsets.ModelViewSet):
         return SpreadingSessionSerializer
 
     def perform_destroy(self, instance):
+        from apps.materials.models import StockTransaction
         year = instance.year
         affected_pairs = {(item.field_id, item.fertilizer_id) for item in instance.items.all()}
+        StockTransaction.objects.filter(spreading_item__session=instance).delete()
         instance.delete()
         sync_actual_bags_for_pairs(year, affected_pairs)
 
@@ -485,6 +487,8 @@ class SpreadingCandidatesView(APIView):
         delivery_queryset = DeliveryTripItem.objects.filter(trip__delivery_plan__year=year)
         if delivery_plan_id:
             delivery_queryset = delivery_queryset.filter(trip__delivery_plan_id=delivery_plan_id)
+        else:
+            delivery_queryset = delivery_queryset.filter(trip__date__isnull=False)
         delivery_rows = delivery_queryset.values(
             'field_id',
             'field__name',

backend/apps/materials/migrations/0004_fix_spreading_item_on_delete.py

@@ -0,0 +1,20 @@
+# Generated by Django 5.0 on 2026-03-17 10:44
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('fertilizer', '0008_spreadingsession_fertilizationentry_actual_bags_and_more'),
+        ('materials', '0003_stocktransaction_spreading_item_and_more'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='stocktransaction',
+            name='spreading_item',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='stock_transactions', to='fertilizer.spreadingsessionitem', verbose_name='散布実績明細'),
+        ),
+    ]

backend/apps/materials/models.py

@@ -207,7 +207,7 @@ class StockTransaction(models.Model):
     )
     spreading_item = models.ForeignKey(
         'fertilizer.SpreadingSessionItem',
-        on_delete=models.CASCADE,
+        on_delete=models.SET_NULL,
         null=True,
         blank=True,
         related_name='stock_transactions',