[BUG] Vietnamese IME input not working on macOS (Telex/VNI)

Description

Cannot type Vietnamese with diacritics using Telex or VNI input methods on macOS. Characters don't compose correctly - the combining/composing characters are either dropped or displayed incorrectly.

Environment

• OS: macOS (Darwin 25.0.0)
• Terminal: Terminal.app / iTerm2
• Locale: C.UTF-8
• Input Method: Vietnamese Telex / VNI

Steps to Reproduce

1. Set macOS keyboard to Vietnamese (Telex or VNI)
2. Run claude in terminal
3. Try to type Vietnamese with diacritics (e.g., "tiếng Việt")
4. Characters don't compose correctly

Expected Behavior

Should be able to type Vietnamese with full diacritics like in any other terminal application.

Actual Behavior

Diacritics don't appear, characters are dropped, or composition doesn't work.

Related Issues

• #44948 - Vietnamese IME on Windows
• #34549 - Vietnamese Unicode diacritics on Windows
• #43381 - IME composition for Vietnamese/Japanese/CJK on Linux
• #7989 - Vietnamese Telex on Windows

Additional Context

This affects all CJK/IME-based input methods on macOS, not just Vietnamese.