fix: get the app building

- settings.gradle.kts: add dependencyResolutionManagement repositories so app deps resolve
- activity_main.xml: move help text with raw quotes to a string resource (commands_help)
- RingService.kt: import NotificationChannel and PendingIntent
- gradle wrapper: add gradlew + gradle-wrapper.jar, regenerate properties
- add .gitignore for build outputs and local.properties

settings.gradle.kts

@@ -6,5 +6,12 @@ pluginManagement {
     }
 }
 
+dependencyResolutionManagement {
+    repositories {
+        google()
+        mavenCentral()
+    }
+}
+
 rootProject.name = "LostMyPhone"
 include(":app")