refactor(core): ai session create (#11539)

Close [BS-3079](https://linear.app/affine-design/issue/BS-3079).

- Separate the create session logic from the `createMessage function`.
- Ensure the session is created before executing any chat or actions.
- Convert the `AIActions` into asynchronous functions.
- Transfer the update prompt name logic to the chat action.
- Introduce a networkSearch field in `AITextActionOptions`.
- Eliminate the redundant `LAST_ROOT_SESSION_ID`.

blocksuite/affine/model/src/elements/mindmap/mindmap.ts

@@ -743,7 +743,7 @@ export class MindmapElementModel extends GfxGroupLikeElementModel<MindmapElement
     const targetPos =
       typeof targetXYWH === 'string' ? deserializeXYWH(targetXYWH) : targetXYWH;
     const offsetX = targetPos[0] - x;
-    const offsetY = targetPos[1] - y + targetPos[3];
+    const offsetY = targetPos[1] - y;
 
     this.surface.doc.transact(() => {
       this.childElements.forEach(el => {