Opt+Arrow word navigation doesn't work with Cyrillic text

Description

When typing in Russian (Cyrillic) in the Claude Code input field, Opt+Left / Opt+Right (word jump) doesn't work correctly — the cursor doesn't move by words as expected. With Latin text it works fine.

Steps to reproduce

1. Open Claude Code in terminal (Ghostty on macOS)
2. Type a message in Russian, e.g. привет как дела
3. Press Opt+Left or Opt+Right to jump by words
4. Cursor doesn't jump by words — it either doesn't move or moves character by character

Expected behavior

Opt+Arrow should jump between Cyrillic words the same way it does with Latin words.

Environment

• macOS (Apple Silicon)
• Ghostty 1.2.3
• zsh
• Claude Code (latest, installed via native installer)