fix: remove invalid null fields from conditionalSwitch node defaults

The customTitle and comment fields are typed as string | undefined in
ConditionalSwitchNodeData. The null values were masked by an 'as' cast
but caused strict type errors. These fields are optional and don't need
explicit defaults.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/store/utils/nodeDefaults.ts

@@ -305,8 +305,6 @@ export const createDefaultNodeData = (type: NodeType): WorkflowNodeData => {
       } as SwitchNodeData;
     case "conditionalSwitch":
       return {
-        customTitle: null,
-        comment: null,
         incomingText: null,
         rules: [
           {