chore(gradle): fix code-review findings on app module setup

- Restore 4-space indent on kotlin-compose plugin alias (regression from
  the previous cleanup commit)
- Fix invalid ProGuard rule: HiltAndroidApp is an annotation type, not
  a class - use '-keep @dagger.hilt.android.HiltAndroidApp class *' to
  actually retain the @HiltAndroidApp-annotated Application
- Remove vectorDrawables.useSupportLibrary - dead config since minSdk 29
  (native VectorDrawable support since API 21)

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

app/build.gradle.kts

@@ -17,7 +17,6 @@ android {
         versionName = "0.1.0"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
-        vectorDrawables { useSupportLibrary = true }
     }
 
     buildTypes {