Voice recorder button should be disabled when model is busy

Fixes ntegrals#32

Disable the voice recorder button when the model is busy.

* Add a `disabled` class to the button when `thinking` is `true`.
* Update the `onClick` handler to prevent further actions if `thinking` is `true`.
* Ensure the button is re-enabled once the assistant finishes processing.

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For more details, open the [Copilot Workspace session](https://copilot-workspace.githubnext.com/ntegrals/aura-voice/issues/32?shareId=XXXX-XXXX-XXXX-XXXX).

src/components/AssistantButton/AssistantButton.tsx

@@ -266,7 +266,8 @@ const AssistantButton: React.FC = () => {
 
           recording ? stopRecording() : startRecording();
         }}
-        className="hover:scale-105 ease-in-out duration-500 hover:cursor-pointer text-[70px]"
+        className={`hover:scale-105 ease-in-out duration-500 hover:cursor-pointer text-[70px] ${thinking ? "disabled" : ""}`}
+        disabled={thinking}
       >
         <div className="rainbow-container">
           <div className="green"></div>