feat: add cloud save backend

prisma/schema/client.prisma

@@ -1,6 +1,7 @@
 enum ClientCapabilities {
     PeerAPI    @map("peerAPI") // other clients can use the HTTP API to P2P with this client
     UserStatus @map("userStatus") // this client can report this user's status (playing, online, etc etc)
+    CloudSaves       @map("cloudSaves") // ability to save to save slots
 }
 
 // References a device
@@ -16,6 +17,8 @@ model Client {
     lastConnected DateTime
 
     peerAPI ClientPeerAPIConfiguration?
+
+    lastAccessedSaves SaveSlot[]
 }
 
 model ClientPeerAPIConfiguration {