refactor(editor): new icon picker (#13658)

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

* **New Features**
* In-tree icon picker for Callout blocks (emoji, app icons, images) with
popup UI and editor-wide extension/service.
* Callout toolbar adds background color presets, an icon-picker action,
and a destructive Delete action.

* **Refactor**
* Replaced legacy emoji workflow with icon-based rendering, updated
state, styling, and lifecycle for callouts.

* **Tests**
  * Updated callout E2E to reflect new default icon and picker behavior.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

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Co-authored-by: L-Sun <zover.v@gmail.com>

packages/frontend/core/src/components/hooks/affine/use-ai-specs.ts

@@ -44,6 +44,7 @@ export const useAISpecs = () => {
       .mobile(framework)
       .electron(framework)
       .linkPreview(framework)
+      .iconPicker(framework)
       .codeBlockPreview(framework).value;
 
     return manager.get('page');