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

build.gradle.kts

@@ -0,0 +1,7 @@
+plugins {
+    alias(libs.plugins.android.application) apply false
+    alias(libs.plugins.kotlin.android) apply false
+    alias(libs.plugins.kotlin.serialization) apply false
+    alias(libs.plugins.compose.compiler) apply false
+    alias(libs.plugins.roborazzi) apply false
+}