Support CJK (Chinese/Japanese/Korean) word boundary navigation with Option+Arrow keys on macOS

Environment

• Platform: macOS (iTerm2)
• Claude Code Version: Latest
• Terminal: iTerm2

Current Behavior

When typing Chinese (or other CJK languages) in Claude Code's input prompt:

• Option + Left/Right Arrow navigates by ASCII words only
• Chinese characters are not recognized as word boundaries
• Navigation treats entire Chinese sentence as one unit

Expected Behavior

Should match native iTerm2 behavior:

• Option + Arrow should jump between Chinese words/phrases
• Respect CJK word boundaries (词边界)
• Consistent with macOS system-wide text navigation

Steps to Reproduce

1. Type a mixed input: hello 你好世界 world
2. Press Option + Left Arrow
3. Cursor jumps over entire Chinese portion, not word-by-word

Technical Context

This appears to be a readline/input library limitation in recognizing CJK character boundaries. The underlying input handler may need:

• Unicode word boundary detection (UAX #29)
• CJK-aware tokenization
• Platform-specific word navigation mappings

Impact

Affects all CJK language users on macOS, making text editing cumbersome for non-ASCII input.

Related

• This works correctly in native iTerm2 shell
• Other modern terminals (VS Code, etc.) support CJK word navigation