Update app.json to enforce dark mode and enhance Android navigation bar styling

- Changed userInterfaceStyle from 'automatic' to 'dark' for consistent theming.
- Added androidNavigationBar configuration with background color and bar style for improved UI on Android devices.

app.json

@@ -6,7 +6,7 @@
     "orientation": "portrait",
     "icon": "./assets/images/icon.png",
     "scheme": "umra",
-    "userInterfaceStyle": "automatic",
+    "userInterfaceStyle": "dark",
     "newArchEnabled": true,
     "splash": {
       "image": "./assets/images/splash-icon.png",
@@ -22,7 +22,11 @@
         "backgroundColor": "#ffffff"
       },
       "edgeToEdgeEnabled": true,
-      "package": "com.nurmuhammet.ali.Umra"
+      "package": "com.nurmuhammet.ali.Umra",
+      "androidNavigationBar": {
+        "backgroundColor": "#1C1C1E",
+        "barStyle": "light-content"
+      }
     },
     "web": {
       "bundler": "metro",