feat: add StorageManager, VisualizationManager, UIManager, EditorManager, and update PanelResizer for improved snippet handling and visualization

src/StorageManager.js

@@ -0,0 +1,16 @@
+import { defaultSnippets } from './config.js';
+
+export class StorageManager {
+    constructor() {
+        this.SNIPPETS_KEY = 'vegaSnippets';
+    }
+
+    loadSnippets() {
+        const stored = localStorage.getItem(this.SNIPPETS_KEY);
+        return stored ? JSON.parse(stored) : defaultSnippets;
+    }
+
+    saveSnippets(snippets) {
+        localStorage.setItem(this.SNIPPETS_KEY, JSON.stringify(snippets));
+    }
+}