fix(select): remove item focus style when there are no selected items only at ionic mode (#30750)

Issue number: resolves #

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This PR introduces improvements to the visual focus styling of Ionic
items when inside a select modal.

## What is the current behavior?
- The CSS variables `--background-focused` and
`--background-focused-opacity` were missing from `item.ionic.scss`,
which resulted in the native default outline focus style being applied
to focused items.
- When no item is selected, the focus style is currently applied to the
first list item by default, which we intend to change.

## What is the new behavior?
- Added missing focus css variables
- Hide the default focus style when there is no item selected

## NOTE
- This change will require an additional interaction to observe the
focus behavior when navigating through keyboard, since tap-based
navigation does not rely on focus styling.

## Does this introduce a breaking change?

- [ ] Yes
- [X] No

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## Other information

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screenshots of how the component looks before and after the change. -->

---------

Co-authored-by: ionitron <hi@ionicframework.com>
Co-authored-by: Maria Hutt <thetaPC@users.noreply.github.com>

core/src/components/select-modal/select-modal.ionic.scss

@@ -67,4 +67,9 @@ ion-content {
   --padding-end: #{globals.$ion-space-400} !important;
   /* stylelint-disable-next-line declaration-no-important */
   --padding-bottom: #{globals.$ion-space-1200} !important;
+
+  // Set the background to the focused element within a radio group only when there is a checked radio
+  &:has(.radio-checked) .ion-focused:not(.item-radio-checked) {
+    --background-focused-opacity: 1;
+  }
 }