feat(core): support ai doc search panel (#9831)

Support issue [BS-2351](https://linear.app/affine-design/issue/BS-2351) and [BS-2461](https://linear.app/affine-design/issue/BS-2461).

## What changed?
- Add `chat-panel-add-popover` component.
- Refactor part of `AtMenuConfigService` into `DocSearchMenuService`.
- Add signal `content` property to `DocChip` interface for markdown content update.

<div class='graphite__hidden'>
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blocksuite/blocks/src/root-block/widgets/index.ts

@@ -30,6 +30,7 @@ export { AffineImageToolbarWidget } from './image-toolbar/index.js';
 export { AffineInnerModalWidget } from './inner-modal/inner-modal.js';
 export * from './keyboard-toolbar/index.js';
 export {
+  type LinkedMenuAction,
   type LinkedMenuGroup,
   type LinkedMenuItem,
   type LinkedWidgetConfig,

blocksuite/blocks/src/root-block/widgets/linked-doc/config.ts

@@ -69,9 +69,11 @@ export type LinkedMenuItem = {
   icon: TemplateResult<1>;
   suffix?: string | TemplateResult<1>;
   // disabled?: boolean;
-  action: () => Promise<void> | void;
+  action: LinkedMenuAction;
 };
 
+export type LinkedMenuAction = () => Promise<void> | void;
+
 export type LinkedMenuGroup = {
   name: string;
   items: LinkedMenuItem[] | Signal<LinkedMenuItem[]>;