feat(app): Koin bootstrap + AppTheme + Material3 XML theme (REDI-84)

- ArchitectureApp.Application: startKoin { androidLogger; androidContext; modules(coreDataModule) }.
  Modules are assembled only here; feature modules will append to the list.
- MainActivity hosts a themed empty screen via AppTheme + AppScaffold (design-system).
- Activity XML theme upgraded to Theme.Material3.DayNight.NoActionBar (Compose themes via AppTheme;
  the Material3 XML theme lets the later Views renderer inherit Material3 styling).
- :app depends on :core:data + :core:design-system; applies the koin convention.

app/build.gradle.kts

@@ -1,13 +1,20 @@
 plugins {
     alias(libs.plugins.architecture.android.application)
     alias(libs.plugins.architecture.compose)
+    alias(libs.plugins.architecture.koin)
 }
 
 dependencies {
+    // :app is the only place modules are assembled and the dependency graph is wired.
+    implementation(project(":core:data"))
+    implementation(project(":core:design-system"))
+
     implementation(libs.androidx.core.ktx)
     implementation(libs.androidx.activity.compose)
     implementation(libs.androidx.lifecycle.runtime.ktx)
     implementation(libs.bundles.lifecycle.compose)
+    // Material Components — required for the Material3 XML Activity theme.
+    implementation(libs.material)
 
     androidTestImplementation(libs.androidx.compose.ui.test.junit4)
     debugImplementation(libs.androidx.compose.ui.test.manifest)