fix: split view focus (#11217)

# After:

https://github.com/user-attachments/assets/990d500d-2da7-488e-ac32-dd7bd229f896

# Before:

https://github.com/user-attachments/assets/6676766a-c76a-414b-a35e-53d2cda10c24

blocksuite/affine/rich-text/src/dom.ts

@@ -68,6 +68,7 @@ export function focusTextModel(
   id: string,
   offset: number = 0
 ) {
+  std.event.active = true;
   selectTextModel(std, id, offset);
 }