fix(android): add kotlin-test test dep for assertEquals/assertNull

AuthCookieInterceptorTest imports `kotlin.test.assertEquals` /
`kotlin.test.assertNull` which weren't resolving without the explicit
kotlin-test dep. `kotlin("test")` is sourced from the applied Kotlin
plugin (built-in via AGP 9), so no version pin needed.

Hilt + KSP code generation worked correctly in the prior run —
hiltAggregateDepsDebug succeeded; the failure was purely test-side.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

android/app/build.gradle.kts

@@ -157,6 +157,9 @@ dependencies {
     testImplementation(libs.mockk)
     testImplementation(libs.kotlinx.coroutines.test)
     testImplementation(libs.okhttp.mockwebserver)
+    // kotlin.test for assertEquals/assertNull/etc. — version managed by
+    // the applied Kotlin plugin so no explicit version pin needed.
+    testImplementation(kotlin("test"))
 
     androidTestImplementation(platform(libs.compose.bom))
     androidTestImplementation(libs.compose.ui.test)