Centre the macOS traffic lights in the 48px title bar

trafficLightPosition.y grows the system title-bar container; the buttons keep
their distance from its bottom edge, so 26 centres them in our bar.

Author: gaoyu06

src-tauri/tauri.macos.conf.json

@@ -13,7 +13,7 @@
         "transparent": true,
         "trafficLightPosition": {
           "x": 18,
-          "y": 17
+          "y": 26
         }
       }
     ]