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/kotlin/com/subtracks/MainActivity.kt

@@ -0,0 +1,20 @@
+package com.subtracks
+
+import android.os.Bundle
+import androidx.activity.ComponentActivity
+import androidx.activity.compose.setContent
+import androidx.activity.enableEdgeToEdge
+import com.subtracks.ui.HelloScreen
+import com.subtracks.ui.theme.SubtracksTheme
+
+class MainActivity : ComponentActivity() {
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        enableEdgeToEdge()
+        setContent {
+            SubtracksTheme {
+                HelloScreen()
+            }
+        }
+    }
+}

app/src/main/kotlin/com/subtracks/SubtracksApp.kt

@@ -0,0 +1,5 @@
+package com.subtracks
+
+import android.app.Application
+
+class SubtracksApp : Application()

app/src/main/kotlin/com/subtracks/ui/HelloScreen.kt

@@ -0,0 +1,53 @@
+package com.subtracks.ui
+
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Surface
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.tooling.preview.Preview
+import androidx.compose.ui.unit.dp
+import com.subtracks.ui.theme.SubtracksTheme
+
+@Composable
+fun HelloScreen(modifier: Modifier = Modifier) {
+    Surface(
+        modifier = modifier.fillMaxSize(),
+        color = MaterialTheme.colorScheme.background,
+    ) {
+        Column(
+            modifier = Modifier
+                .fillMaxSize()
+                .padding(24.dp),
+            verticalArrangement = Arrangement.Center,
+            horizontalAlignment = Alignment.CenterHorizontally,
+        ) {
+            Text(
+                text = "Subtracks",
+                style = MaterialTheme.typography.headlineLarge,
+                color = MaterialTheme.colorScheme.onBackground,
+            )
+            Spacer(Modifier.height(8.dp))
+            Text(
+                text = "Kotlin / Jetpack Compose rewrite",
+                style = MaterialTheme.typography.bodyMedium,
+                color = MaterialTheme.colorScheme.onSurfaceVariant,
+            )
+        }
+    }
+}
+
+@Preview
+@Composable
+private fun HelloScreenPreview() {
+    SubtracksTheme {
+        HelloScreen()
+    }
+}

app/src/main/kotlin/com/subtracks/ui/theme/Color.kt

@@ -0,0 +1,11 @@
+package com.subtracks.ui.theme
+
+import androidx.compose.ui.graphics.Color
+
+val Purple80 = Color(0xFFD0BCFF)
+val PurpleGrey80 = Color(0xFFCCC2DC)
+val Pink80 = Color(0xFFEFB8C8)
+
+val Purple40 = Color(0xFF6650A4)
+val PurpleGrey40 = Color(0xFF625B71)
+val Pink40 = Color(0xFF7D5260)

app/src/main/kotlin/com/subtracks/ui/theme/Theme.kt

@@ -0,0 +1,20 @@
+package com.subtracks.ui.theme
+
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.darkColorScheme
+import androidx.compose.runtime.Composable
+
+private val SubtracksDarkColorScheme = darkColorScheme(
+    primary = Purple80,
+    secondary = PurpleGrey80,
+    tertiary = Pink80,
+)
+
+@Composable
+fun SubtracksTheme(content: @Composable () -> Unit) {
+    MaterialTheme(
+        colorScheme = SubtracksDarkColorScheme,
+        typography = SubtracksTypography,
+        content = content,
+    )
+}

app/src/main/kotlin/com/subtracks/ui/theme/Type.kt

@@ -0,0 +1,12 @@
+package com.subtracks.ui.theme
+
+import androidx.compose.material3.Typography
+import androidx.compose.ui.text.font.FontWeight
+
+val SubtracksTypography = Typography().let { base ->
+    base.copy(
+        headlineLarge = base.headlineLarge.copy(fontWeight = FontWeight.W800),
+        headlineMedium = base.headlineMedium.copy(fontWeight = FontWeight.W700),
+        headlineSmall = base.headlineSmall.copy(fontWeight = FontWeight.W600),
+    )
+}