fix(properties-panel): enhance element detection and error handling for nested structures

test/elements/test-noprops.ts

@@ -0,0 +1,37 @@
+import {
+  DeesElement,
+  customElement,
+  type TemplateResult,
+  html,
+  css,
+} from '@design.estate/dees-element';
+
+@customElement('test-noprops')
+export class TestNoProps extends DeesElement {
+  public static demo = () => html`<test-noprops></test-noprops>`;
+
+  public static styles = [
+    css`
+      :host {
+        display: block;
+        padding: 20px;
+        background: #f0f0f0;
+        border: 2px solid #ccc;
+        border-radius: 8px;
+      }
+      .message {
+        font-family: monospace;
+        color: #666;
+      }
+    `
+  ];
+
+  public render() {
+    return html`
+      <div class="message">
+        This element has no @property decorators.
+        Properties panel should handle this gracefully.
+      </div>
+    `;
+  }
+}