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
