A snappier editor

Improved

• Editor performance — eliminated typing lag in the prose editor. Characters appear as fast as you type, even in long chapters.
• App icon — refreshed PNG with proper transparent squircle corners at every size macOS expects.

Fixed

• Swift concurrency warnings under MainActor default isolation — cleaner builds and fewer edge-case threading surprises.
• Critical and major code-review findings across document handling, scene actions, and export paths.
• All unit tests brought back to green, including demo document fixtures used in UI scenarios.