Make Claude Code better behaved w.r.t. job control signals (including SIGTSTP)

Description

Application doesn't respond to Ctrl-Z to suspend/background.

Steps to reproduce

1. Launch application in terminal
2. Press Ctrl-Z
3. Application remains in foreground

Expected behaviour

Application should suspend and return to shell prompt.

Environment

• OS: macOS
• Shell: wezterm
• Claude CLI version: 0.2.53

Additional Information

Terminal settings show SUSP is set to ^Z (verified with stty -a).
Other applications respond correctly to Ctrl-Z in same terminal.