refactor: convert AmountInput to function props

- Convert AmountInput from @Emit("update:value") to onUpdateValue function prop
- Update GiftDetailsStep to use new function prop interface for amount handling

AmountInput now provides better parent control over validation and updates

src/components/ContactInputForm.vue

@@ -111,8 +111,6 @@ export default class ContactInputForm extends Vue {
   @Prop({ type: Function, default: () => {} })
   onNavigateOnboardMeeting!: () => void | Promise<void>;
 
-
-
   /**
    * Function prop for handling model value updates
    * Called when the input value changes for v-model binding