Fix mobile app submodule initialization and cleanup

- Removed incorrect swingmusic_mobile directory
- Properly initialized swingmusic_mobile submodule from swingmusic-mobile.git
- Clean submodule configuration for unified release workflow

swingmusic_mobile/ios/RunnerTests/RunnerTests.swift

@@ -1,12 +0,0 @@
-import Flutter
-import UIKit
-import XCTest
-
-class RunnerTests: XCTestCase {
-
-  func testExample() {
-    // If you add code to the Runner application, consider adding tests here.
-    // See https://developer.apple.com/documentation/xctest for more information about using XCTest.
-  }
-
-}