start kotlin/jetpack compose rewrite

replace the flutter project with a gradle/compose android app:
- nix flake dev shell (jdk21, android sdk 35, build-tools 37, gradle)
- material3 app with a placeholder screen
- roborazzi/robolectric screenshot tests with one golden
- carry over the existing launcher/notification assets

app/src/main/res/values/ic_launcher_background.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <color name="ic_launcher_background">#6A1B9A</color>
+</resources>

app/src/main/res/values/strings.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <string name="app_name">Subtracks</string>
+</resources>

app/src/main/res/values/themes.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <style name="Theme.Subtracks" parent="android:Theme.Material.NoActionBar">
+        <item name="android:windowBackground">@android:color/black</item>
+        <item name="android:statusBarColor">@android:color/transparent</item>
+        <item name="android:navigationBarColor">@android:color/transparent</item>
+    </style>
+</resources>