Make modal interaction states take exclusive control over inputs

All keys should be blocked from going to other things (global shortcuts, switching tools, etc.) while a modal action is ongoing (a modal action includes dragging with a tool, G/R/S, etc.).

This will fix a very various bugs/edge cases where an ongoing interaction state can be interrupted by pressing a random key, such as one that might group the selected layers or change tools.

*Not a good beginner issue.*

No files or tests are identified. Start by tracing modal interaction states and the input-dispatch path, including dragging and G/R/S actions, then determine how global shortcuts and tool switching are reached. Done means every key is exclusively handled by an ongoing modal action and cannot interrupt it.

Rédigé par le modèle d'indexation à partir du texte de l'issue.