fix broken exposed ref access when adding custom validation rules

`defineExpose` unwraps refs, so `searchQuery.value` was `undefined` and
`hasUnfinishedParameters` threw inside the `added` handler. Previously the
rule had already been added by the time the error was swallowed; now
`added` is emitted before the selection lands, so the throw aborted it.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0146FsnrtqFd6RhsnrEDf7Fy

Author: duncanmcclean

resources/js/components/field-validation/Builder.vue

@@ -256,8 +256,9 @@ export default {
 
         ifSearchNotFoundAddCustom() {
             let rulesSelect = this.$refs.rulesSelect;
-            let rule = rulesSelect.searchQuery.value;
+            let rule = rulesSelect?.searchQuery;
 
+            if (!rule) return;
             if (this.searchNotFound(rulesSelect) || this.hasUnfinishedParameters(rule)) return;
 
             this.add(rule);
@@ -272,7 +273,7 @@ export default {
         },
 
         searchNotFound(rulesSelect) {
-            return rulesSelect.searchQuery.value?.length === 0 || rulesSelect?.filteredOptions.length === 0;
+            return rulesSelect.filteredOptions.length === 0;
         },
 
         updated(rules) {