[BUG] Edit tool removes executable permission from shell scripts

Description

When using the Edit tool to modify a shell script that has executable permissions (chmod +x), the file loses its executable bit after the edit is applied.

Steps to Reproduce

1. Have a shell script with executable permissions (e.g., bin/script.sh with mode 755)
2. Use the Edit tool to make a change to the file
3. Check file permissions after edit

Expected Behavior

The Edit tool should preserve existing file permissions (including the executable bit).

Actual Behavior

The executable permission is stripped from the file after editing.

Environment

• Platform: Linux
• Claude Code version: latest

Additional Context

This is problematic for shell scripts, Makefiles, and other files that need to retain executable permissions.