feat: add cloud save backend

prisma/schema/app.prisma

@@ -3,6 +3,10 @@ model ApplicationSettings {
 
     enabledAuthencationMechanisms AuthMec[]
     metadataProviders             String[]
+
+    saveSlotCountLimit   Int   @default(5)
+    saveSlotSizeLimit    Float @default(10) // MB
+    saveSlotHistoryLimit Int   @default(3)
 }
 
 enum Platform {