fix: remove invalid null fields from conditionalSwitch quickstart default

The customTitle and comment fields are typed as string | undefined, not
string | null. Remove them from the quickstart default data to fix the
TypeScript build error.

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

src/lib/quickstart/validation.ts

@@ -401,8 +401,6 @@ function createDefaultNodeData(type: NodeType): WorkflowNodeData {
       return { inputType: null, switches: [{ id: "sw-1", name: "Output 1", enabled: true }] };
     case "conditionalSwitch":
       return {
-        customTitle: null,
-        comment: null,
         incomingText: null,
         rules: [
           {