chore: bump version to 0.2.1, update README for TUI redesign

- Document 4-tab layout (Dashboard, Studio, Shell, Config)
- Add keyboard shortcuts table for new tabs
- Update version references from 0.2.0 to 0.2.1

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

internal/version/version.go

@@ -2,7 +2,7 @@ package version
 
 const (
 	Name    = "muyue"
-	Version = "0.2.0"
+	Version = "0.2.1"
 	Author  = "La Légion de Muyue"
 	License = "MIT"
 )