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/tests/vueNodes/widgets/int/integerWidget.spec.ts

@@ -0,0 +1,42 @@
+import {
+  comfyExpect as expect,
+  comfyPageFixture as test
+} from '../../../../fixtures/ComfyPage'
+
+test.describe('Vue Integer Widget', () => {
+  test.beforeEach(async ({ comfyPage }) => {
+    await comfyPage.setSetting('Comfy.VueNodes.Enabled', true)
+    await comfyPage.setup()
+  })
+
+  test('should be disabled and not allow changing value when link connected to slot', async ({
+    comfyPage
+  }) => {
+    await comfyPage.loadWorkflow('vueNodes/linked-int-widget')
+    await comfyPage.vueNodes.waitForNodes()
+
+    const seedWidget = comfyPage.vueNodes.getWidgetByName('KSampler', 'seed')
+    const controls = comfyPage.vueNodes.getInputNumberControls(seedWidget)
+    const initialValue = Number(await controls.input.inputValue())
+
+    // Verify widget is disabled when linked
+    await controls.incrementButton.click({ force: true })
+    await expect(controls.input).toHaveValue(initialValue.toString())
+
+    await controls.decrementButton.click({ force: true })
+    await expect(controls.input).toHaveValue(initialValue.toString())
+
+    await expect(seedWidget).toBeVisible()
+
+    // Delete the node that is linked to the slot (freeing up the widget)
+    await comfyPage.vueNodes.getNodeByTitle('Int').click()
+    await comfyPage.vueNodes.deleteSelected()
+
+    // Test widget works when unlinked
+    await controls.incrementButton.click()
+    await expect(controls.input).toHaveValue((initialValue + 1).toString())
+
+    await controls.decrementButton.click()
+    await expect(controls.input).toHaveValue(initialValue.toString())
+  })
+})