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.