test infra: JUnit5 unit tests on Android modules + Compose UI test wiring

Add an architecture.android.unit.test convention plugin that runs local unit
tests on the JUnit5 platform via useJUnitPlatform() (AndroidUnitTest extends
Gradle's Test) + the unit-test bundle. Deliberately NOT using the
de.mannodermaus plugin (targets AGP 8.x; we're on AGP 9). Add
junit-platform-launcher (Gradle 9 dropped the bundled launcher); set the
instrumentation runner; add a compose-ui-test bundle pinning espresso/runner to
current versions (transitive espresso 3.5.0 calls the removed
InputManager.getInstance() on API 34+). CI now runs ./gradlew test and compiles
the instrumented tests. Drop unused testing catalog entries.

feature/characters/presentation/build.gradle.kts

@@ -1,6 +1,7 @@
 plugins {
     alias(libs.plugins.architecture.android.library)
     alias(libs.plugins.architecture.koin)
+    alias(libs.plugins.architecture.android.unit.test)
 }
 
 // UI-agnostic presentation: the MVI ViewModel + State/Action/Event live here and are shared by