refactor: implement cross-platform abstraction for process management, media control, and startup configuration (TESTING)

internal/linux/overlay.go

@@ -0,0 +1,15 @@
+//go:build linux
+package linux
+
+// linuxOverlay provides a simple dummy implementation for Linux.
+// It relies on tray icon status updates for visual feedback instead of raw drawing.
+type linuxOverlay struct{}
+
+func NewOverlay() *linuxOverlay {
+	return &linuxOverlay{}
+}
+
+func (o *linuxOverlay) Show(message string)   {}
+func (o *linuxOverlay) Hide()                 {}
+func (o *linuxOverlay) SetVolume(level float64) {}
+func (o *linuxOverlay) Close()                {}