feat: grant signup bonus points

apps/billing/models.py

@@ -248,6 +248,7 @@ class PointsLedger(models.Model):
         CONSUME = "consume", "消费"
         ADJUST = "adjust", "调整"
         REFUND = "refund", "退款"
+        SIGNUP_BONUS = "signup_bonus", "注册赠点"
 
     user = models.ForeignKey(
         settings.AUTH_USER_MODEL,
@@ -307,3 +308,32 @@ class PointsLedger(models.Model):
         super().clean()
         if self.change_type == self.ChangeType.ADJUST and not (self.reason or "").strip():
             raise ValidationError({"reason": "Adjust ledger entries require a reason."})
+
+
+class SignupBonusGrant(models.Model):
+    user = models.OneToOneField(
+        settings.AUTH_USER_MODEL,
+        verbose_name="用户",
+        on_delete=models.PROTECT,
+        related_name="signup_bonus_grant",
+    )
+    points_granted = models.BigIntegerField("赠送点数", default=100)
+    created_at = models.DateTimeField("创建时间", auto_now_add=True)
+
+    class Meta:
+        db_table = "signup_bonus_grant"
+        verbose_name = "注册赠点记录"
+        verbose_name_plural = "注册赠点记录"
+        ordering = ("-created_at", "-id")
+        constraints = [
+            models.CheckConstraint(
+                condition=Q(points_granted__gt=0),
+                name="signup_bonus_grant_points_positive",
+            ),
+        ]
+        indexes = [
+            models.Index(fields=("user", "created_at")),
+        ]
+
+    def __str__(self) -> str:
+        return f"{self.user} signup bonus: {self.points_granted}"