fix(editor): centerize iframe modal in mobile (#13073)

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[BS-3160](https://linear.app/affine-design/issue/BS-3160/新的-embed-输入的-sheet-没有弹起来)

#### PR Dependency Tree


* **PR #13073** 👈

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

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

## Summary by CodeRabbit

* **Bug Fixes**
* Improved popup positioning and responsiveness when using virtual
keyboards, ensuring popups remain visible and correctly placed above the
keyboard.
* Standardized how popups and overlays are created and referenced
throughout the app, reducing inconsistencies and potential display
issues.
* Enhanced stability of date picker, AI panels, and slash menu popovers
by refining how their elements are managed and updated.

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

packages/frontend/core/src/blocksuite/ai/actions/doc-handler.ts

@@ -305,6 +305,6 @@ export function handleInlineAskAIAction(
       },
       abortController: abortController,
       closeOnClickAway: true,
-    });
+    }).portal;
   }, 0);
 }

packages/frontend/core/src/blocksuite/ai/components/ask-ai-toolbar.ts

@@ -65,7 +65,7 @@ export class AskAIToolbarButton extends WithDisposable(LitElement) {
       },
       abortController: this._abortController,
       closeOnClickAway: true,
-    });
+    }).portal;
   };
 
   private readonly _generateAnswer: AffineAIPanelWidgetConfig['generateAnswer'] =