Implement persistent hardcore death bans (XUID + IP) for dedicated server

On the dedicated server, hardcore death now persists XUID and IP bans to
banned-players.json and banned-ips.json via the Access system, and
disconnects the player. Bans survive server restarts. Client-hosted games
retain the existing in-memory XUID ban with force-save behavior.

- Add hardcore property to server.properties (forces Hard difficulty)
- Add LevelData::setHardcore() so loaded worlds respect the server config
- Add PlayerList::banPlayerForHardcoreDeath() with persistent XUID + IP bans
- Reject respawn requests server-side in hardcore mode
- Ensure server-side player ticks run without move packets (fixes
  environmental damage not applying for some clients)
- Restore 0x8 hardcore bit on LoginPacket/RespawnPacket wire format so
  the client-side death screen detects hardcore mode correctly

Minecraft.World/DerivedLevelData.cpp

@@ -180,6 +180,10 @@ bool DerivedLevelData::isHardcore()
 	return wrapped->isHardcore();
 }
 
+void DerivedLevelData::setHardcore(bool hardcore)
+{
+}
+
 LevelType *DerivedLevelData::getGenerator()
 {
 	return wrapped->getGenerator();