[Bug] Ctrl+Z suspend functionality broken in v2.1.0+

Bug Description
Ctrl+Z (suspend) stopped working after upgrading to v2.1.0+. Other keyboard shortcuts (Ctrl+C, Ctrl+B, Shift+Enter) work correctly.

Environment Info

• Platform: darwin
• Terminal: ghostty
• Version: 2.1.1
• Feedback ID: f6386dff-9c45-4db4-a973-a799022dcfa0

Expected behavior:
Pressing Ctrl+Z should suspend Claude Code process (resumable with fg), as documented in v0.2.44 changelog.

Actual behavior:
Ctrl+Z has no effect. The key press is ignored.

Suspected cause:
The v2.1.0 change "Shift+Enter works out of the box in iTerm2, WezTerm, Ghostty, and Kitty" likely modified terminal keyboard mode handling. This may have changed how Ctrl+Z keycode is received, causing the internal key mapping to fail.

Reproduction steps:

1. Run claude in Ghostty terminal
2. Press Ctrl+Z
3. Observe: nothing happens (should suspend)

Additional context:

• stty -a in normal shell shows isig enabled and susp = ^Z correctly configured
• Custom statusLine configured in settings.json (may or may not be related)
• Issue may be Ghostty-specific or affect all terminals with new keyboard mode handling