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.

索引モデルが issue の本文から書いたものです。