Improve comment for Sender interface

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

Author: silv-io

internal/output/tui_sink.go

@@ -1,9 +1,10 @@
 package output
 
-// Sender is implemented by bubbletea Program and test doubles.
+// Sender abstracts Bubble Tea's Program.Send to keep TUISink decoupled and testable.
 type Sender interface {
 	Send(msg any)
 }
+}
 
 type TUISink struct {
 	sender Sender