[BUG] Chinese characters display as question marks in Termius terminal on Linux

Bug Description

Chinese (CJK) characters display as question marks (?) in the Claude Code TUI when accessed through Termius SSH client on Linux. The issue does not occur in local terminal sessions with proper UTF-8 font support.

Environment

• OS: Kali GNU/Linux Rolling 2025.4
• Claude Code version: 2.1.139
• Node.js: v24.13.1
• Terminal: Termius (SSH client, macOS -> Linux)
• TERM: xterm-256color
• Locale: en_US.UTF-8 (all LC_* variables set correctly)
• Shell: fish

Steps to Reproduce

1. Connect to a Linux server via Termius SSH
2. Run claude
3. Ask Claude to output Chinese text (e.g., "用中文回答")
4. Chinese characters render as ??? or question mark placeholders

Expected Behavior

Chinese characters should render correctly, same as they do in local terminal sessions.

Additional Context

• Locale is properly configured (en_US.UTF-8), and Chinese text renders fine in regular terminal commands (e.g., echo "中文测试" works correctly in the same Termius session)
• The issue is specific to Claude Code's TUI rendering, not the terminal itself
• Similar issue reported for Cyrillic: #57994
• Related CJK encoding issue: #56946

Possible Cause

Claude Code's TUI (Ink/React-based) may not be passing through CJK characters correctly when the terminal font doesn't provide full Unicode coverage, or the TUI's character width calculation may be mishandling CJK double-width characters.