fix(ios): button group is the system segmented control

[SRWieZ]

On iOS, native:button-group draws its own row of buttons, while Android uses Material's segmented button row. So the same Blade looks like a native control on Android and like a custom widget on iOS, and iOS users lose what the system control gives: sliding across segments, the system animation, and VoiceOver reading "Medium, button, 2 of 3, selected".

This PR renders it as a UISegmentedControl. Nothing changes on the PHP side (options, value, @change, disabled, a11y-label), and the same tab-change event is sent. The selected segment uses primary with onPrimary text, like Android, and labels keep the theme font at fontSm, scaled with Dynamic Type. A server value we just sent doesn't move the selection back, as before.

Apps that use the group on iOS will see the system look instead of the bordered row.

To reproduce:

<native:column class="w-full px-4 pt-6 gap-6">
    <native:button-group class="w-full" :options="['Small', 'Medium', 'Large']" :value="$size" @change="pickSize" />
    <native:button-group class="w-full" :options="['List', 'Grid']" :value="$view" @change="pickView" />
    <native:button-group class="w-full" :options="['Day', 'Week', 'Month']" :value="0" disabled />
</native:column>

public int $size = 1;

public int $view = 0;

public function pickSize(int $index): void
{
    $this->size = $index;
}

public function pickView(int $index): void
{
    $this->view = $index;
}

iOS before and after (iPhone 17 Pro simulator, iOS 26), with Android for comparison: