Add Capacitor Android project and native Tiptoi plugin

Checked-in android/ Capacitor project plus the native TiptoiPlugin
(Kotlin): SAF directory picker for the pen, listing/copying/deleting
.gme files on the pen, and downloading GME/cover files into
app-private storage.

client/android/variables.gradle

@@ -0,0 +1,16 @@
+ext {
+    minSdkVersion = 23
+    compileSdkVersion = 35
+    targetSdkVersion = 35
+    androidxActivityVersion = '1.9.2'
+    androidxAppCompatVersion = '1.7.0'
+    androidxCoordinatorLayoutVersion = '1.2.0'
+    androidxCoreVersion = '1.15.0'
+    androidxFragmentVersion = '1.8.4'
+    coreSplashScreenVersion = '1.0.1'
+    androidxWebkitVersion = '1.12.1'
+    junitVersion = '4.13.2'
+    androidxJunitVersion = '1.2.1'
+    androidxEspressoCoreVersion = '3.6.1'
+    cordovaAndroidVersion = '10.1.1'
+}