feat(core): add SoftDeleteMixin to db base, TenantMixin inherits from it

app/core/db/__init__.py

@@ -30,6 +30,14 @@ class Base(DeclarativeBase):
         return self.__name__.lower() + "s"
 
 
+class SoftDeleteMixin:
+    """Adds deleted_at column for soft-delete support."""
+
+    deleted_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True, default=None
+    )
+
+
 class TimestampMixin:
     """Adds created_at and updated_at timestamps."""
 
@@ -41,7 +49,7 @@ class TimestampMixin:
     )
 
 
-class TenantMixin(TimestampMixin):
+class TenantMixin(TimestampMixin, SoftDeleteMixin):
     """Adds tenant_id column and enables ORM-level auto-filtering."""
 
     tenant_id: Mapped[uuid.UUID] = mapped_column(PGUUID(as_uuid=True), nullable=False, index=True)