Addresses feedback on PR #78 review comment. The test BitSelectField_Should_Render_Option_Group_Disabled_If_Disabled_Property_Is_Set_To_True() claimed to verify disabled option groups but neither set the property nor asserted the rendered attribute.

Changes:

• Set Disabled="true" on first BitSelectItemGroup in test component
• Assert disabled attribute on corresponding <optgroup> in expected markup

<BitSelectItemGroup Label="Group 1" Disabled="true">
    <BitSelectItem TValue="string" Value="@("value 1")">value 1</BitSelectItem>
    <BitSelectItem TValue="string" Value="@("value 2")">value 2</BitSelectItem>
</BitSelectItemGroup>

Expected markup now correctly validates:

<optgroup label="Group 1" disabled>
    <option value="value 1">value 1</option>
    <option value="value 2"> value 2</option>
</optgroup>

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.