OmniBuild Wand

Adds /wand export - share your builds as schematics!

• New client command: /wand export [name] saves the structure currently copied in your wand to .minecraft/schematics/ as a .litematic file, ready to share with friends (or open in Litematica). Omit the name for an automatic timestamped name.
• Works for both small and large copied structures, and for blueprints loaded via /wand load.
• Exports the original orientation; only block states are stored (no chest contents / sign text), matching Copy behavior.

中文：新增 /wand export 指令——把你复制的建筑导出成蓝图分享！

• 新客户端指令 /wand export <名字>：把手杖里当前复制的结构导出成 .litematic 文件，存到 .minecraft/schematics/，可直接发给好友或用 Litematica 打开（不写名字会自动用时间戳命名）。
• 大小结构都支持，/wand load 加载进来的蓝图也能再导出。
• 导出的是原始朝向；只记录方块本身，不含箱子物品 / 告示牌文字（与复制行为一致）。