chore: remove obsolete Android app configuration files

- Deleted build.gradle.kts, gradle.properties, and gradlew files as part of the cleanup process.
- Removed local.properties and various generated files from the .gradle directory to streamline the project structure.
- Cleared out unnecessary build artifacts and intermediate files to improve project maintainability.

mobile-app/build.gradle.kts

@@ -0,0 +1,9 @@
+plugins {
+    // this is necessary to avoid the plugins to be loaded multiple times
+    // in each subproject's classloader
+    alias(libs.plugins.androidApplication) apply false
+    alias(libs.plugins.androidLibrary) apply false
+    alias(libs.plugins.jetbrainsCompose) apply false
+    alias(libs.plugins.compose.compiler) apply false
+    alias(libs.plugins.kotlinMultiplatform) apply false
+}