Harden the mod against hostile servers and players

- PacketReader for all network data: lengths are checked against the real data
  (Mono allocated the claimed size first - a fake 2 GB length crashed the game)
- FsmSync: remote players can no longer switch arbitrary FSMs - never PLAYER /
  Systems / MSCO objects, CLICK only on FSMs that wait for a click, bolt/assembly
  events only along a transition the FSM really has for that event
- Time/weather (msco.world) and '* ' system-style chat only from the host in P2P
  (the dedicated server filters them itself); other msco.* ids are reserved

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ServerBrowser.cs

@@ -244,7 +244,7 @@ namespace MSCO
                     byte[] payload = ReadExactly(stream, length - 1);
                     info.Ping = (int)watch.ElapsedMilliseconds;
 
-                    using (var r = new BinaryReader(new MemoryStream(payload)))
+                    using (var r = new PacketReader(payload))
                     {
                         info.Name = r.ReadString();
                         info.Description = r.ReadString();