Fix label/slot precedence

[ganyicz]

The scenario

A user-land component wrapping Flux components passes a label prop:

<x-select label="Industry" />

{{-- resources/views/components/select.blade.php --}}
@props(['label'])

<flux:select :$label variant="listbox">
    <flux:select.option>Photography</flux:select.option>
    <flux:select.option>Design services</flux:select.option>
</flux:select>

The problem

The label prop leaks from the parent component into all children.

This happens because <flux:delegate-component> forwards inherited data from the entire component stack.

Combined with {{ $label ?? $slot }}, every option displays "Industry".

The solution

Reverse the priority from {{ $label ?? $slot }} to {{ $slot->isNotEmpty() ? $slot : $label }} across 9 files where this pattern occurs. Slot content now wins when present; label prop still works as fallback for self-closing tags.

Risk assessment

• The $slot->isNotEmpty() pattern is already used elsewhere in the codebase
• The docs never show both being passed simultaneously
• Self-closing tags (<flux:radio label="Foo" />) produce an empty slot, so $label is still used as fallback

The problematic pattern would be:

<flux:menu.radio label="Foo">Bar</flux:menu.radio>

Before this change: Renders Foo
After this change: Renders Bar

Flux Pro PR: livewire/flux-pro#436

Fixes #2300