feat: add app icon;

feat: add app to tray;

README.md

@@ -71,6 +71,13 @@ Queue / retry:
 
 - Run `ytpl-sync.exe` (GUI).
 
+## Tray
+
+- The app supports minimizing to tray on close if the OS provides a system tray; use the tray icon menu to quit.
+- Tray behavior settings (Settings page):
+  - `close_to_tray`: close hides to tray (keeps running).
+  - `minimize_to_tray`: minimize hides to tray.
+
 ## Data & Layout
 
 - Database: `db/app.db`