在庫管理機能 Phase 1 実装（apps/materials + フロントエンド）

Backend:
- apps/materials 新規作成（Material, FertilizerProfile, PesticideProfile, StockTransaction）
- 資材マスタ CRUD API（/api/materials/materials/）
- 入出庫履歴 API（/api/materials/stock-transactions/）
- 在庫集計 API（/api/materials/stock-summary/）
- 既存 Fertilizer に material OneToOneField 追加（0005マイグレーション、データ移行込み）

Frontend:
- /materials: 在庫一覧画面（タブフィルタ、履歴展開、入出庫モーダル）
- /materials/masters: 資材マスタ管理（肥料/農薬/その他タブ、インライン編集）
- Navbar に「在庫管理」メニュー追加
- Material/StockTransaction/StockSummary 型定義追加

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

backend/apps/fertilizer/migrations/0005_fertilizer_material.py

@@ -0,0 +1,56 @@
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+def create_materials_for_existing_fertilizers(apps, schema_editor):
+    Fertilizer = apps.get_model('fertilizer', 'Fertilizer')
+    Material = apps.get_model('materials', 'Material')
+    FertilizerProfile = apps.get_model('materials', 'FertilizerProfile')
+
+    for fertilizer in Fertilizer.objects.all():
+        material = Material.objects.create(
+            name=fertilizer.name,
+            material_type='fertilizer',
+            maker=fertilizer.maker or '',
+            stock_unit='bag',
+            is_active=True,
+            notes=fertilizer.notes or '',
+        )
+        FertilizerProfile.objects.create(
+            material=material,
+            capacity_kg=fertilizer.capacity_kg,
+            nitrogen_pct=fertilizer.nitrogen_pct,
+            phosphorus_pct=fertilizer.phosphorus_pct,
+            potassium_pct=fertilizer.potassium_pct,
+        )
+        fertilizer.material = material
+        fertilizer.save(update_fields=['material'])
+
+
+def reverse_migration(apps, schema_editor):
+    Fertilizer = apps.get_model('fertilizer', 'Fertilizer')
+    Fertilizer.objects.all().update(material=None)
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('fertilizer', '0004_fertilizationplan_calc_settings'),
+        ('materials', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='fertilizer',
+            name='material',
+            field=models.OneToOneField(
+                blank=True,
+                null=True,
+                on_delete=django.db.models.deletion.SET_NULL,
+                related_name='legacy_fertilizer',
+                to='materials.material',
+                verbose_name='資材マスタ',
+            ),
+        ),
+        migrations.RunPython(create_materials_for_existing_fertilizers, reverse_migration),
+    ]