feat: add levee work records

backend/apps/levee_work/models.py

@@ -0,0 +1,59 @@
+from django.db import models
+
+
+class LeveeWorkSession(models.Model):
+    year = models.IntegerField(verbose_name='年度')
+    date = models.DateField(verbose_name='畔塗日')
+    title = models.CharField(max_length=100, default='水稲畔塗', verbose_name='タイトル')
+    notes = models.TextField(blank=True, default='', verbose_name='備考')
+    created_at = models.DateTimeField(auto_now_add=True)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        verbose_name = '畔塗記録'
+        verbose_name_plural = '畔塗記録'
+        ordering = ['-date', '-id']
+
+    def __str__(self):
+        return f'{self.date} {self.title}'
+
+
+class LeveeWorkSessionItem(models.Model):
+    session = models.ForeignKey(
+        LeveeWorkSession,
+        on_delete=models.CASCADE,
+        related_name='items',
+        verbose_name='畔塗記録',
+    )
+    field = models.ForeignKey(
+        'fields.Field',
+        on_delete=models.PROTECT,
+        verbose_name='圃場',
+    )
+    plan = models.ForeignKey(
+        'plans.Plan',
+        on_delete=models.SET_NULL,
+        null=True,
+        blank=True,
+        related_name='+',
+        verbose_name='作付け計画',
+    )
+    crop_name_snapshot = models.CharField(max_length=100, verbose_name='作物名スナップショット')
+    variety_name_snapshot = models.CharField(
+        max_length=100,
+        blank=True,
+        default='',
+        verbose_name='品種名スナップショット',
+    )
+    created_at = models.DateTimeField(auto_now_add=True)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        verbose_name = '畔塗対象圃場'
+        verbose_name_plural = '畔塗対象圃場'
+        unique_together = [['session', 'field']]
+        ordering = ['field__display_order', 'field__id']
+
+    def __str__(self):
+        return f'{self.session} / {self.field.name}'
+