[BUG] @ file picker does not support diacritic-insensitive search on macOS

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

The @ file picker has inconsistent Unicode matching for accented filenames.
For a file named "Spécifications fonctionnelles.txt":

• Typing @ alone: file does not appear
• Typing @spé (with accent, NFC): file does not appear
• Typing @spe (without accent): file appears correctly

The picker works with the ASCII equivalent but fails with the actual
accented character, which is counterintuitive.

What Should Happen?

Typing @ alone should list the file.
Typing @spé (with accent) should match "Spécifications fonctionnelles.txt".
This is likely a Unicode normalization issue: macOS APFS stores filenames
in NFD form (decomposed), while keyboard input produces NFC form (composed).
The picker should normalize both strings before comparing.

Error Messages/Logs

Steps to Reproduce

1. Create a file named "Spécifications fonctionnelles.txt" on macOS
2. Type @ in the Claude Code input → file does not appear
3. Type @spé (with accent é) → file does not appear
4. Type @spe (without accent) → file appears correctly

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.73

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_