Add ChoicesManager plugin for enhanced dropdown handling:

- Introduce `choices_manager.js` for initializing and managing custom dropdowns with `Choices` library.
- Implement options parsing and initialization with i18n support.
- Provide methods for managing instances including init, destroy, and refresh.

src/autometabuilder/web/static/js/plugins/choices_manager.js

@@ -0,0 +1,66 @@
+/**
+ * AutoMetabuilder - Choices Manager
+ */
+(() => {
+    const i18n = (key, fallback = '') => window.AMBContext?.t?.(key, fallback) || fallback || key;
+
+    const ChoicesManager = {
+        instances: [],
+
+        init() {
+            this.initAll();
+        },
+
+        initAll() {
+            document.querySelectorAll('[data-choices]').forEach(el => {
+                if (el.dataset.choicesInit === 'true') return;
+
+                const optionsStr = el.dataset.choicesOptions || '{}';
+                let options = {};
+                try {
+                    options = JSON.parse(optionsStr);
+                } catch (error) {
+                    console.warn('Invalid choices options:', optionsStr);
+                }
+
+                const instance = new Choices(el, {
+                    searchEnabled: true,
+                    shouldSort: false,
+                    allowHTML: false,
+                    removeItemButton: options.removeItemButton || false,
+                    placeholder: true,
+                    placeholderValue: el.dataset.placeholder || i18n('ui.common.select_placeholder', 'Select...'),
+                    searchPlaceholderValue: i18n('ui.choices.search_placeholder', 'Type to search...'),
+                    noResultsText: i18n('ui.choices.no_results', 'No results found'),
+                    noChoicesText: i18n('ui.choices.no_choices', 'No choices available'),
+                    ...options
+                });
+                el.dataset.choicesInit = 'true';
+                this.instances.push(instance);
+            });
+        },
+
+        destroy() {
+            this.instances.forEach(instance => {
+                try {
+                    const element = instance.passedElement?.element;
+                    if (element) {
+                        element.dataset.choicesInit = 'false';
+                    }
+                    instance.destroy();
+                } catch (error) {
+                    // Ignore errors from already destroyed instances
+                }
+            });
+            this.instances = [];
+        },
+
+        refresh() {
+            this.destroy();
+            this.initAll();
+        }
+    };
+
+    window.ChoicesManager = ChoicesManager;
+    window.AMBPlugins?.register('choices_manager', async () => ChoicesManager.init());
+})();