Keep host-only LAN admin commands for Hardcore mode,blockself-cheating only

Hardcore mode blocks cheats, Creative and Spectator mode entirely. This makes moderation impossible for multiplayer Hardcore servers, as admins need Spectator mode to detect X-Ray cheats and Creative mode for world maintenance, which cannot be done in Survival mode.

Proposal:

Add a Hardcore-only experimental toggle in experimental gameplay settings: Enable admin Creative/Spectator access.

1. Only visible in Hardcore worlds, available to enable any time even on existing saves.

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2. Once enabled, cannot be turned off again permanently.

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3. Only server OPs can switch game modes; regular players stay bound to original Hardcore rules.

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4. 用户对因启用此实验性选项而导致的世界崩溃或损坏承担全部责任。

这一变化保持了单人硬核模式的原样，同时为服务器所有者提供了官方管理工具，风险则由服务器端承担。