chore: configure :app module gradle build

Compose with Material 3 Expressive (1.5.0-alpha21 explicit override of
BOM stable), Hilt 2.59.2 + KSP 2.3.9, DataStore. Single-module project.
JVM 17 + Kotlin 2.3.21. JUnit Jupiter 6.1.0 unified (jupiter + platform).
testOptions opts into JUnit Platform so JUnit5/6 tests get discovered.

Note: kotlin-android plugin removed — AGP 9.0+ provides built-in Kotlin
support and the plugin now hard-errors when applied alongside AGP 9.x.
kotlin-compose plugin retained (separate Compose compiler plugin).

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

app/proguard-rules.pro

@@ -0,0 +1,6 @@
+# Keep Hilt-generated classes
+-keep class dagger.hilt.** { *; }
+-keep class * extends dagger.hilt.android.HiltAndroidApp
+
+# Compose Compiler may keep its own; defaults are fine
+-dontwarn org.jetbrains.annotations.**