fix Vue node widgets should be in disabled state if their slots are connected with a link (#5834)

## Summary

Fixes https://github.com/Comfy-Org/ComfyUI_frontend/issues/5692 by
making widget link connection status trigger on change so Vue widgets
with connected links could properly switch to the `disabled` state when
they are implicitly converted to inputs.

## Changes

- **What**: Added `node:slot-links:changed` event tracking and reactive
slot data synchronization for Vue widgets

```mermaid
graph TD
    A[Widget Link Change] --> B[NodeInputSlot.link setter]
    B --> C{Is Widget Input?}
    C -->|Yes| D[Trigger slot-links:changed]
    C -->|No| E[End]
    D --> F[Graph Event Handler]
    F --> G[syncNodeSlotData]
    G --> H[Update Vue Reactive Data]
    H --> I[Widget Re-render]
    
    style A fill:#f9f9f9,stroke:#333,color:#000
    style I fill:#f9f9f9,stroke:#333,color:#000
```

## Review Focus

Widget reactivity performance with frequent link changes and event
handler memory management in graph operations.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5834-fix-Vue-node-widgets-should-be-in-disabled-state-if-their-slots-are-connected-with-a-link-27c6d73d365081f6a6c3c1ddc3905c5e)
by [Unito](https://www.unito.io)

browser_tests/fixtures/VueNodeHelpers.ts

@@ -119,4 +119,24 @@ export class VueNodeHelpers {
       await this.page.waitForSelector('[data-node-id]')
     }
   }
+
+  /**
+   * Get a specific widget by node title and widget name
+   */
+  getWidgetByName(nodeTitle: string, widgetName: string): Locator {
+    return this.getNodeByTitle(nodeTitle).locator(
+      `_vue=[widget.name="${widgetName}"]`
+    )
+  }
+
+  /**
+   * Get controls for input number widgets (increment/decrement buttons and input)
+   */
+  getInputNumberControls(widget: Locator) {
+    return {
+      input: widget.locator('input'),
+      incrementButton: widget.locator('button').first(),
+      decrementButton: widget.locator('button').last()
+    }
+  }
 }