Command Block UI Overhaul

Bug Fixes

• Fixed layout using the original text after truncation.
• Fixed repeated responder calls and temporary cursor jumps to the end during insertion or deletion.
• Fixed layout and cursor state not updating when the maximum length is reduced.
• Fixed incorrect word-deletion offsets and Unicode truncation splitting surrogate pairs.
• Fixed mouse positioning offsets caused by incorrect padding.
• Fixed cursor visibility and suggestion popup positioning after Tab completion.
• Fixed incomplete suggestion background coverage and overlapping usage or error messages.
• Fixed suggestion list overflow, incorrect scrolling near the last entry, and right-click applying suggestions.
• Fixed stale asynchronous completions overriding newer input, reopening dismissed suggestions, and updating the UI outside the client thread.
• Fixed Enter saving before initialization completes and resizing incorrectly enabling controls.
• Fixed unrelated or subsequent command block packets affecting the current draft.
• Fixed the output toggle directly modifying client-side block state.
• Fixed narration potentially accessing an uninitialized object.
• Optimized multiline storage and cursor position calculations to reduce unnecessary traversal and temporary objects.

New Features

• Undo/redo: stores up to 100 edit snapshots, restoring text, cursor, and selection; new edits clear the redo history.
• Multiline mouse drag selection with automatic edge scrolling.
• Preserves editing state and undo history when resizing the window.
• Suggestion popups stay within screen bounds and open upwards when needed.

已修复的问题

• 修复文本截断后仍使用原始文本排版的问题。
• 修复插入、删除时重复触发 responder，以及光标临时跳到全文末尾的问题。
• 修复缩短最大长度后未更新排版和光标的问题。
• 修复单词删除偏移计算错误，以及 Unicode 截断可能拆开代理对的问题。
• 修复鼠标定位的内边距偏差。
• 修复 Tab 补全后光标可见区域和建议窗口位置未同步的问题。
• 修复建议窗口背景遮挡不完整、多条用法或错误提示重叠的问题。
• 修复建议列表越界、滚动末项偏差，以及右键误应用建议的问题。
• 修复旧异步补全覆盖新输入、关闭后重新弹出，以及回调线程不受限的问题。
• 修复未加载完成时可按 Enter 保存，以及窗口缩放错误启用控件的问题。
• 修复无关或后续命令方块数据包影响当前编辑内容的问题。
• 修复输出开关直接修改客户端方块状态的问题。
• 修复初始化阶段旁白可能访问空对象的问题。
• 优化多行容器和光标位置计算，减少不必要的遍历与临时对象。

新功能

• 撤销/重做：最多保存 100 次编辑快照，恢复文本、光标和选区；新修改清空重做记录。
• 支持鼠标多行拖选和边缘自动滚动。
• 窗口缩放保留编辑状态和撤销历史。
• 建议窗口支持屏幕边界限制和自动向上展开。