fix(tests): handle missing schemathesis gracefully in API contract tests

- Replaced `pytest.mark.skipif` with `pytest.skip` to better manage scenarios where `schemathesis` is not installed.
- Added a fallback test function to ensure explicit handling for missing dependencies.

backend/tests/e2e/test_api_contracts.py

@@ -27,13 +27,16 @@ except ImportError:
 pytestmark = [
     pytest.mark.e2e,
     pytest.mark.schemathesis,
-    pytest.mark.skipif(
-        not SCHEMATHESIS_AVAILABLE,
-        reason="schemathesis not installed - run: make install-e2e",
-    ),
 ]
 
 
+if not SCHEMATHESIS_AVAILABLE:
+
+    def test_schemathesis_compatibility():
+        """Gracefully handle missing schemathesis dependency."""
+        pytest.skip("schemathesis not installed - run: make install-e2e")
+
+
 if SCHEMATHESIS_AVAILABLE:
     from app.main import app