fix(proguard): keep no-arg constructor of Room *_Impl classes

R8 in playBenchmark (minifyEnabled) stripped the no-arg <init> from
WorkDatabase_Impl because -keepnames preserves names but not members.
Room instantiates generated *_Impl subclasses reflectively via
Class.getDeclaredConstructor(), so startup crashed with
NoSuchMethodException in androidx.startup.InitializationProvider.

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

amethyst/proguard-rules.pro

@@ -63,3 +63,9 @@
 -keep class com.vitorpamplona.quartz.** { *; }
 -keep class com.vitorpamplona.amethyst.** { *; }
 -keep class com.vitorpamplona.ammolite.** { *; }
+
+# Room generates *_Impl subclasses instantiated reflectively via no-arg constructor.
+# -keepnames preserves the name but R8 still strips the unused <init>().
+-keep class * extends androidx.room.RoomDatabase {
+    <init>();
+}