feat(editor): add start-with-ai button for empty doc (#9836)

Close [BS-2391](https://linear.app/affine-design/issue/BS-2391/bs-ai-toolbar-空状态下添加-actions-列表)

https://github.com/user-attachments/assets/cbded517-2d3d-4a75-b144-644e2b03f68a

packages/frontend/core/src/components/blocksuite/block-suite-editor/starter-bar.tsx

@@ -1,3 +1,5 @@
+import { handleInlineAskAIAction } from '@affine/core/blocksuite/presets/ai';
+import { pageAIGroups } from '@affine/core/blocksuite/presets/ai/_common/config';
 import { DocsService } from '@affine/core/modules/doc';
 import { EditorService } from '@affine/core/modules/editor';
 import { FeatureFlagService } from '@affine/core/modules/feature-flag';
@@ -5,6 +7,7 @@ import { TemplateDocService } from '@affine/core/modules/template-doc';
 import { TemplateListMenu } from '@affine/core/modules/template-doc/view/template-list-menu';
 import { useI18n } from '@affine/i18n';
 import track from '@affine/track';
+import { PageRootBlockComponent } from '@blocksuite/affine/blocks';
 import type { Store } from '@blocksuite/affine/store';
 import {
   AiIcon,
@@ -62,6 +65,7 @@ const StarterBarNotEmpty = ({ doc }: { doc: Store }) => {
       [doc.id, templateDocService.list]
     )
   );
+  const enableAI = useLiveData(featureFlagService.flags.enable_ai.$);
   const enableTemplateDoc = useLiveData(
     featureFlagService.flags.enable_template_doc.$
   );
@@ -85,10 +89,29 @@ const StarterBarNotEmpty = ({ doc }: { doc: Store }) => {
     setTemplateMenuOpen(open);
   }, []);
 
-  const showAI = false;
+  const startWithAI = useCallback(() => {
+    const std = editorService.editor.editorContainer$.value?.std;
+    if (!std) return;
+
+    const rootBlockId = std.host.doc.root?.id;
+    if (!rootBlockId) return;
+
+    const rootComponent = std.view.getBlock(rootBlockId);
+    if (!(rootComponent instanceof PageRootBlockComponent)) return;
+
+    const { id, created } = rootComponent.focusFirstParagraph();
+    if (created) {
+      std.view.viewUpdated.once(v => {
+        if (v.id === id) handleInlineAskAIAction(std.host, pageAIGroups);
+      });
+    } else {
+      handleInlineAskAIAction(std.host, pageAIGroups);
+    }
+  }, [editorService.editor]);
+
   const showTemplate = !isTemplate && enableTemplateDoc;
 
-  if (!showAI && !showTemplate) {
+  if (!enableAI && !showTemplate) {
     return null;
   }
 
@@ -96,10 +119,12 @@ const StarterBarNotEmpty = ({ doc }: { doc: Store }) => {
     <div className={styles.root}>
       {t['com.affine.page-starter-bar.start']()}
       <ul className={styles.badges}>
-        {showAI ? (
+        {enableAI ? (
           <Badge
+            data-testid="start-with-ai-badge"
             icon={<AiIcon />}
             text={t['com.affine.page-starter-bar.ai']()}
+            onClick={startWithAI}
           />
         ) : null}