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/proguard-rules.pro

@@ -1,6 +1,6 @@
 # Keep Hilt-generated classes
 -keep class dagger.hilt.** { *; }
--keep class * extends dagger.hilt.android.HiltAndroidApp
+-keep @dagger.hilt.android.HiltAndroidApp class *
 
 # Compose Compiler may keep its own; defaults are fine
 -dontwarn org.jetbrains.annotations.**