refactor: split database model tests into organized modules

Split the monolithic test_database_models.py into focused test modules:

Database model tests (tests/unit/models/database/):
- test_customer.py: Customer model and authentication tests
- test_inventory.py: Inventory model tests
- test_marketplace_import_job.py: Import job model tests
- test_marketplace_product.py: Marketplace product model tests
- test_order.py: Order and OrderItem model tests
- test_product.py: Product model tests
- test_team.py: Team invitation and membership tests
- test_user.py: User model tests
- test_vendor.py: Vendor model tests

Schema validation tests (tests/unit/models/schema/):
- test_auth.py: Auth schema validation tests
- test_customer.py: Customer schema validation tests
- test_inventory.py: Inventory schema validation tests
- test_marketplace_import_job.py: Import job schema tests
- test_order.py: Order schema validation tests
- test_product.py: Product schema validation tests

This improves test organization and makes it easier to find
and maintain tests for specific models.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tests/unit/models/database/test_user.py

@@ -0,0 +1,104 @@
+# tests/unit/models/database/test_user.py
+"""Unit tests for User database model."""
+import pytest
+from sqlalchemy.exc import IntegrityError
+
+from models.database.user import User
+
+
+@pytest.mark.unit
+@pytest.mark.database
+class TestUserModel:
+    """Test User model."""
+
+    def test_user_creation(self, db):
+        """Test User model creation and relationships."""
+        user = User(
+            email="db_test@example.com",
+            username="dbtest",
+            hashed_password="hashed_password_123",
+            role="user",
+            is_active=True,
+        )
+
+        db.add(user)
+        db.commit()
+        db.refresh(user)
+
+        assert user.id is not None
+        assert user.email == "db_test@example.com"
+        assert user.username == "dbtest"
+        assert user.role == "user"
+        assert user.is_active is True
+        assert user.created_at is not None
+        assert user.updated_at is not None
+
+    def test_user_email_uniqueness(self, db):
+        """Test email unique constraint."""
+        user1 = User(
+            email="unique@example.com",
+            username="user1",
+            hashed_password="hash1",
+        )
+        db.add(user1)
+        db.commit()
+
+        # Duplicate email should raise error
+        with pytest.raises(IntegrityError):
+            user2 = User(
+                email="unique@example.com",
+                username="user2",
+                hashed_password="hash2",
+            )
+            db.add(user2)
+            db.commit()
+
+    def test_user_username_uniqueness(self, db):
+        """Test username unique constraint."""
+        user1 = User(
+            email="user1@example.com",
+            username="sameusername",
+            hashed_password="hash1",
+        )
+        db.add(user1)
+        db.commit()
+
+        # Duplicate username should raise error
+        with pytest.raises(IntegrityError):
+            user2 = User(
+                email="user2@example.com",
+                username="sameusername",
+                hashed_password="hash2",
+            )
+            db.add(user2)
+            db.commit()
+
+    def test_user_default_values(self, db):
+        """Test User model default values."""
+        user = User(
+            email="defaults@example.com",
+            username="defaultuser",
+            hashed_password="hash",
+        )
+        db.add(user)
+        db.commit()
+        db.refresh(user)
+
+        assert user.is_active is True  # Default
+        assert user.role == "vendor"  # Default (UserRole.VENDOR)
+
+    def test_user_optional_fields(self, db):
+        """Test User model with optional fields."""
+        user = User(
+            email="optional@example.com",
+            username="optionaluser",
+            hashed_password="hash",
+            first_name="John",
+            last_name="Doe",
+        )
+        db.add(user)
+        db.commit()
+        db.refresh(user)
+
+        assert user.first_name == "John"
+        assert user.last_name == "Doe"