Multiple platform instances allowed when plugin is marked as single-instance
### Describe The Bug

### What is happening?

The plugin Virtual accessories For Homebridge is marked as a single-instance plugin:

<img width="467" alt="Image" src="https://github.com/user-attachments/assets/905a2c49-1e32-4ddb-960b-5686d47db0ae" /><p>

However, accessing the JSON configuration from the plugin menu ...

<img width="665" alt="Image" src="https://github.com/user-attachments/assets/007eaf59-88ad-4d8d-bd0b-5e86a7bb2c59" /><p>

... allows for creating multiple instances:

<img width="808" alt="Image" src="https://github.com/user-attachments/assets/b304fe42-b02c-4479-a51e-eeb24156533e" /><p>

<img width="807" alt="Image" src="https://github.com/user-attachments/assets/262be5d3-798d-4881-8f2b-a52afa0a5ffc" /><p>

As the user sees this functionality available and it is not displayed anywhere that the plugin is single-instance, they may choose to create multiple instances resulting in unexpected and unstable plugin behavior, as it expects the to be the only instance.

### What you expect to happen?

The Homebridge UI should respect the plugin configuration and not allow adding a new instance if the plugin configuration marks it as a single-instance platform.


### Logs

N/A

### Config

```JSON
{
  "pluginAlias": "VirtualAccessoriesForHomebridge",
  "pluginType": "platform",
  "singular": true,
  "footerDisplay": "* = required fields",
  "strictValidation": true,
  "schema": {
  ...
  }
}
```

### Homebridge UI Version

v5.0.0-beta.51

### Homebridge Version

v1.9.0

### Node.js Version

v22.12.0

### Operating System

macOS

### Environment Info

Using hb-service

### Raspberry Pi Model

None