Keep reflective Room database constructors (#1109)

Minified `legacy` and `lollipop` builds can fail to initialize WorkManager during background sync with `InstantiationException` / `NoSuchMethodException`. With **AGP 9.4.1 / R8 9.4.24** strict full-mode keep semantics, Room 2.5.0/2.6.1 consumer rules keep database classes but allow removal of the public no-argument constructor used by reflection, including `WorkDatabase_Impl()`.

Author: iMiKED

app/src/preMarshmallow/proguard-rules.pro

@@ -0,0 +1,5 @@
+# @MadeByLLM("gpt-6-astra")
+# Room 2.5.0/2.6.1 consumer rules omit the constructor used by reflection.
+-keepclassmembers class * extends androidx.room.RoomDatabase {
+  public <init>();
+}