fix: correct tooling versions (Gradle 9.5.1, AGP 8.13.2) and add Kotlin Compose plugin

- AGP 2.1.3 doesn't exist; use 8.13.2 (latest stable 8.x)
- Gradle 9.6.1 incompatible with AGP 8.x; use 9.5.1
- Add org.jetbrains.kotlin.plugin.compose (required since Compose MP 1.6.10)
- Fix source set access (by getting) and iOS Darwin dependency injection
- Remove instrumentedTestVariant (KotlinSourceSetTree unresolved)

gradle/libs.versions.toml

@@ -1,7 +1,7 @@
 [versions]
 kotlin = "2.2.20"
 compose-multiplatform = "1.11.1"
-agp = "2.1.3"
+agp = "8.13.2"
 ktor = "3.5.1"
 kotlinx-serialization-json = "1.11.0"
 kotlinx-coroutines = "1.11.0"
@@ -27,6 +27,7 @@ androidx-activity-compose = { module = "androidx.activity:activity-compose", ver
 
 [plugins]
 kotlin-multiplatform = { id = "org.jetbrains.kotlin.multiplatform", version.ref = "kotlin" }
+kotlin-compose = { id = "org.jetbrains.kotlin.plugin.compose", version.ref = "kotlin" }
 compose-multiplatform = { id = "org.jetbrains.compose", version.ref = "compose-multiplatform" }
 kotlin-serialization = { id = "org.jetbrains.kotlin.plugin.serialization", version.ref = "kotlin" }
 android-application = { id = "com.android.application", version.ref = "agp" }

gradle/wrapper/gradle-wrapper.properties

@@ -1,6 +1,6 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-9.6.1-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.5.1-bin.zip
 networkTimeout=10000
 retries=0
 retryBackOffMs=500