refactor: move app to monorepo

frontend/app/android/build.gradle

@@ -0,0 +1,33 @@
+// Top-level build file where you can add configuration options common to all sub-projects/modules.
+
+buildscript {
+    
+    repositories {
+        google()
+        mavenCentral()
+    }
+    dependencies {
+        classpath 'com.android.tools.build:gradle:7.2.1'
+        classpath 'com.google.gms:google-services:4.3.13'
+
+        // NOTE: Do not place your application dependencies here; they belong
+        // in the individual module build.gradle files
+    }
+}
+
+apply from: "variables.gradle"
+
+allprojects {
+    repositories {
+        google()
+        mavenCentral()
+        // https://github.com/transistorsoft/capacitor-background-fetch/blob/master/example/android/build.gradle
+        maven {
+            url("${project(':transistorsoft-capacitor-background-fetch').projectDir}/libs")
+        }
+    }
+}
+
+task clean(type: Delete) {
+    delete rootProject.buildDir
+}