Metro: enable contributesAsInject option.

plugins/src/main/kotlin/extension/DependencyInjectionExtensions.kt

@@ -7,6 +7,7 @@
 
 package extension
 
+import dev.zacsweers.metro.gradle.MetroPluginExtension
 import org.gradle.accessors.dm.LibrariesForLibs
 import org.gradle.api.Project
 import org.gradle.api.provider.Provider
@@ -25,6 +26,9 @@ fun Project.setupDependencyInjection(
     // Apply Metro plugin and configure it
     applyPluginIfNeeded(libs.plugins.metro)
 
+    val metroExtension = extensions.getByName("metro") as MetroPluginExtension
+    metroExtension.contributesAsInject.value(true)
+
     if (generateNodeFactories) {
         applyPluginIfNeeded(libs.plugins.ksp)