[Bug] CJK wide characters cause right-aligned timestamps to misalign in TUI

Bug Description

When Claude Code renders Korean (CJK) text, the right-aligned timestamps on each message line become misaligned. The timestamps drift out of sync with their corresponding content lines, and text wraps at unexpected positions. This occurs because CJK full-width characters occupy 2 terminal columns each, but the TUI's line-width calculation appears to count them as 1 column.

Steps to Reproduce

1. Run Claude Code inside tmux on macOS
2. Interact in Korean (or any CJK language)
3. Observe the right-side timestamps — they no longer align with the message lines they belong to

Expected Behavior

Right-aligned timestamps should remain on the same line as their corresponding message content, regardless of whether the text contains CJK wide characters.

Actual Behavior

• Timestamps on the right side drift and misalign with content lines
• Claude Code's own output wraps across more lines than expected
• Korean text overflows past the timestamp column and gets clipped/hidden behind it
• Text extends beyond the intended content box boundary
• The misalignment persists even on fullscreen (270+ columns)

Screenshots

_Screenshots will be attached in comments below._

Environment

• Claude Code: v2.1.42
• Model: Opus 4.6
• OS: macOS Darwin 25.3.0
• Terminal: tmux inside Terminal.app
• Locale: en_US.UTF-8 (all LC_* variables)
• tmux window size: 270x76 (fullscreen), also reproduced at 109x35
• Language: Korean

Related Issues

• #23534 — CJK full-width characters clipped at right terminal edge (closed, similar root cause)
• #17297 — UTF-8 String Indexing Panic with CJK Characters
• #19118 — Missing Documentation for CJK Character Support

Notes

This appears to be a different manifestation of the same underlying CJK wcwidth calculation issue as #23534. The clipping bug was fixed, but the width miscalculation still affects the right-aligned timestamp positioning and line wrapping logic.