Build fixes + unit tests for Sprint 1

- Fix settings.gradle.kts (dependencyResolutionManagement)
- Add gradle-wrapper.properties + gradle.properties
- Defer Firebase/FCM to Sprint 2 (no google-services.json yet)
- Add placeholder ic_clippy drawable
- Add test deps (JUnit, coroutines-test)
- VoiceStateMachineTest: 14 tests covering happy path, interruption, cancellation, invalid transitions, reset
- ResponseDedupTest: basic dedup cache tests
- Add kotlinx-serialization plugin for Ktor

app/build.gradle.kts

@@ -1,7 +1,9 @@
 plugins {
     id("com.android.application")
     id("org.jetbrains.kotlin.android")
-    id("com.google.gms.google-services")
+    id("org.jetbrains.kotlin.plugin.serialization")
+    // Firebase deferred to Sprint 2
+    // id("com.google.gms.google-services")
 }
 
 android {
@@ -38,9 +40,9 @@ dependencies {
     implementation("androidx.car.app:app:1.7.0")
     implementation("androidx.car.app:app-projected:1.7.0")
 
-    // Firebase Cloud Messaging
-    implementation(platform("com.google.firebase:firebase-bom:33.9.0"))
-    implementation("com.google.firebase:firebase-messaging-ktx")
+    // Firebase Cloud Messaging — Sprint 2
+    // implementation(platform("com.google.firebase:firebase-bom:33.9.0"))
+    // implementation("com.google.firebase:firebase-messaging-ktx")
 
     // HTTP client for Matrix REST API
     implementation("io.ktor:ktor-client-okhttp:3.0.3")
@@ -63,4 +65,8 @@ dependencies {
     // Core
     implementation("androidx.core:core-ktx:1.15.0")
     implementation("androidx.appcompat:appcompat:1.7.0")
+
+    // Testing
+    testImplementation("junit:junit:4.13.2")
+    testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.9.0")
 }