Switching between editing and selecting a pod in Google Slides style

[forrestbao]

We need two modes: editing mode and command mode. In command mode, you can move/delete pods/scopes (via keyboard shortcuts preferrably).

Google Slides or PPT sets the precedent when handling textboxes: if you single-click in the center, then it's editing model. If you single-click around the edge, then it's command mode. In the command mode, the cursor becomes a 4-arrow.

https://github.com/codepod-io/codepod/assets/438579/458b12fc-801d-46e2-91f0-b5618de7936b