fix crash: bump Room version to 2, enable destructive migration

Room crashed on launch with schema hash mismatch because
MessageEntity gained reasoning+sources fields but the DB version
stayed at 1. fallbackToDestructiveMigration(false) only covered
downgrades, not same-version schema changes.

Fix: version 1→2, fallbackToDestructiveMigration(true) so any
future schema change auto-wipes the cache (it's a read-cache,
server is source of truth, rebuilds on next fetch).

app/src/main/java/dev/kaizen/app/db/KaizenDatabase.kt

@@ -8,7 +8,7 @@ import androidx.room.TypeConverters
 
 @Database(
     entities = [ConversationEntity::class, MessageEntity::class],
-    version = 1,
+    version = 2,
     exportSchema = false,
 )
 @TypeConverters(Converters::class)
@@ -26,7 +26,7 @@ abstract class KaizenDatabase : RoomDatabase() {
                     KaizenDatabase::class.java,
                     "kaizen-cache",
                 )
-                .fallbackToDestructiveMigration(false)
+                .fallbackToDestructiveMigration(true)
                 .build()
                 .also { instance = it }
             }