fix: prevent self-clear of field_code in visibility condition repeater

[erikpach]

Summary

Fixes a bug in the visibility conditions UI for custom fields where selecting a value in the Field (field_code) Select inside the conditions Repeater immediately clears the selection.

Reproduction

1. Open Custom Fields management page.
2. Edit any field (or section).
3. Set Visibility mode to anything that requires conditions (e.g. Visible when).
4. Inside the conditions Repeater, pick a value in the Field select.
5. The select clears itself instantly. The user cannot save a working condition.

The bug also affects the ConditionSource::ModelAttribute source where the dropdown of model attributes appears, gets selected, and disappears.

Root cause

src/Filament/Management/Forms/Components/VisibilityComponent.php line 127:

$schema[] = Select::make('field_code')
    ...
    ->afterStateUpdated(fn (Get $get, Set $set) => $this->resetConditionValues($get, $set))

resetConditionValues() is shared with the source Select and contains:

private function resetConditionValues(?Get $get, Set $set): void
{
    $this->clearAllValueFields($set);
    $set('field_code', null); // wipes the user's freshly selected value
    ...
}

So when the user picks field_code, Filament fires afterStateUpdated, which sets field_code back to null.

Fix

Split the reset path:

• resetConditionValues() keeps its current behavior and remains the callback for the source Select (it should clear field_code when the source switches).
• New resetValuesAndOperator() is used by the field_code Select. It only clears the value fields and resets the operator to the first compatible option. It does not touch field_code.

Verification

• Existing test suite passes (654 passed).
• Manual reproduction confirmed before / after.