UpdateWorkflowVersionStep returns client input step without position validation

https://sonarly.com/issue/4115?type=bug

The UpdateWorkflowVersionStep mutation returns the raw client input step as the GraphQL response without merging position data from the existing step or validating the position object, causing a non-nullable field violation when position is present but incomplete.

Fix: ## Fix: Normalize `position` before returning and persisting the updated step

The root cause is that `updateWorkflowVersionStep` returns the raw client input step (via `enrichOutputSchema`, which is a no-op for non-ITERATOR types) directly as the GraphQL mutation response. When the client sends a `position` object that is present but incomplete (e.g. `{}` or `{x: null}`), the GraphQL executor throws `Cannot return null for non-nullable field WorkflowStepPosition.x` because the schema defines `x: Float!` as non-nullable.

The fix adds a `resolvedPosition` check after `updatedStep` is obtained: if `updatedStep.position` is defined but `x` or `y` is not, fall back to `existingStep.position` (the step stored in the DB). This uses the already-imported `isDefined` utility. The `normalizedUpdatedStep` is then used both for persisting to the DB (`updatedSteps`) and as the return value, also fixing the secondary issue of position data loss during persistence.

```typescript file=packages/twenty-server/src/modules/workflow/workflow-builder/workflow-version-step/workflow-version-step-update.workspace-service.ts lines=76-105
    const resolvedPosition =
      isDefined(updatedStep.position) &&
      isDefined(updatedStep.position.x) &&
      isDefined(updatedStep.position.y)
        ? updatedStep.position
        : existingStep.position;

    const normalizedUpdatedStep = { ...updatedStep, position: resolvedPosition };

    const updatedSteps = workflowVersion.steps.map((existingStep) => {
      if (existingStep.id === step.id) {
        return normalizedUpdatedStep;
      } else {
        return existingStep;
      }
    });
    ...
    return normalizedUpdatedStep;
```

This mirrors the pattern already used in `updateWorkflowVersionStepType`, which explicitly sets `position: existingStep.position` when building the updated step.

packages/twenty-server/src/modules/workflow/workflow-builder/workflow-version-step/workflow-version-step-update.workspace-service.ts

@@ -73,9 +73,18 @@ export class WorkflowVersionStepUpdateWorkspaceService {
           additionalCreatedSteps: undefined,
         };
 
+    const resolvedPosition =
+      isDefined(updatedStep.position) &&
+      isDefined(updatedStep.position.x) &&
+      isDefined(updatedStep.position.y)
+        ? updatedStep.position
+        : existingStep.position;
+
+    const normalizedUpdatedStep = { ...updatedStep, position: resolvedPosition };
+
     const updatedSteps = workflowVersion.steps.map((existingStep) => {
       if (existingStep.id === step.id) {
-        return updatedStep;
+        return normalizedUpdatedStep;
       } else {
         return existingStep;
       }
@@ -93,7 +102,7 @@ export class WorkflowVersionStepUpdateWorkspaceService {
       },
     );
 
-    return updatedStep;
+    return normalizedUpdatedStep;
   }
 
   private async updateWorkflowVersionStepType({