chore(ui): remove dead toast and clipboard code

Remove 8 unused exports from clipboard package:
- CopyToClipboardWithMessage, IsClipboardSupported
- ToastMsg, ToastType, ToastInfo, ToastSuccess, ToastWarning, ToastError

These were remnants of a toast notification feature that was never
wired up. No callers exist anywhere in the codebase.

internal/ui/clipboard/clipboard.go

@@ -1,8 +1,6 @@
 package clipboard
 
 import (
-	"runtime"
-
 	tea "charm.land/bubbletea/v2"
 	"github.com/atotto/clipboard"
 )
@@ -26,45 +24,3 @@ func CopyToClipboard(text string) tea.Cmd {
 		},
 	)
 }
-
-// CopyToClipboardWithMessage writes text to clipboard and returns a toast notification.
-func CopyToClipboardWithMessage(text string, message string) tea.Cmd {
-	if text == "" {
-		return nil
-	}
-
-	return tea.Sequence(
-		CopyToClipboard(text),
-		func() tea.Msg {
-			return ToastMsg{Message: message, Type: ToastInfo}
-		},
-	)
-}
-
-// ToastType represents the type of toast notification.
-type ToastType int
-
-const (
-	ToastInfo ToastType = iota
-	ToastSuccess
-	ToastWarning
-	ToastError
-)
-
-// ToastMsg is a message to display a toast notification.
-type ToastMsg struct {
-	Message string
-	Type    ToastType
-}
-
-// IsClipboardSupported returns true if the clipboard is supported on this platform.
-func IsClipboardSupported() bool {
-	switch runtime.GOOS {
-	case "darwin", "windows":
-		return true
-	case "linux":
-		return true
-	default:
-		return false
-	}
-}