feat(core): open artifacts tools automatically (#13668)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **New Features**
* The AI Artifact Tool now auto-opens its preview panel as soon as it
loads, giving immediate visibility without extra clicks.
* The preview initializes proactively and remains in sync as data
updates, streamlining the workflow and reducing setup friction.
* Improves first-use experience by ensuring the preview is ready and
visible on connection, enhancing responsiveness and clarity.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/frontend/core/src/blocksuite/ai/components/ai-tools/artifact-tool.ts

@@ -160,6 +160,12 @@ export abstract class ArtifactTool<
     `;
   }
 
+  override connectedCallback() {
+    super.connectedCallback();
+    // open the preview panel immediately
+    this.openOrUpdatePreviewPanel();
+  }
+
   override render() {
     const err = this.getErrorTemplate();
     if (err) {