fix: add missing ProGuard rules to prevent release build crash

R8 minification was stripping/renaming classes needed at runtime:
private @Serializable ImageEntry, enum valueOf() names, Ktor internals,
and ViewModel constructors.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

android/app/proguard-rules.pro

@@ -1,6 +1,50 @@
+# ========================
+# kotlinx.serialization
+# ========================
 -keepattributes *Annotation*, InnerClasses
 -dontnote kotlinx.serialization.AnnotationsKt
+
 -keepclassmembers class kotlinx.serialization.json.** { *** Companion; }
+
+# Keep @Serializable classes and their generated serializers
+-keepclassmembers @kotlinx.serialization.Serializable class ** {
+    *** Companion;
+    *** INSTANCE;
+    kotlinx.serialization.KSerializer serializer(...);
+}
 -keepclasseswithmembers class io.picoclaw.android.** {
     kotlinx.serialization.KSerializer serializer(...);
 }
+
+# Keep generated $$serializer classes
+-keepclassmembers class io.picoclaw.android.**$$serializer {
+    *** INSTANCE;
+    *;
+}
+
+# Keep private ImageEntry used via Json.decodeFromString in MessageMapper
+-keep class io.picoclaw.android.core.data.mapper.ImageEntry { *; }
+
+# ========================
+# Enums stored as strings in Room DB
+# ========================
+-keepclassmembers enum io.picoclaw.android.core.domain.model.MessageSender { *; }
+-keepclassmembers enum io.picoclaw.android.core.domain.model.MessageStatus { *; }
+
+# ========================
+# Ktor
+# ========================
+-keep class io.ktor.** { *; }
+-keepclassmembers class io.ktor.** { volatile <fields>; }
+-dontwarn io.ktor.**
+
+# ========================
+# OkHttp / Okio
+# ========================
+-dontwarn okhttp3.**
+-dontwarn okio.**
+
+# ========================
+# Koin / ViewModels
+# ========================
+-keep class * extends androidx.lifecycle.ViewModel { <init>(...); }