Shift/Ctrl/Cmd+Enter broken for chat:newline after recent update - only Option+Enter works

Description

Chat input keybindings for newline are broken after the recent Claude Code Instructions update today. Only Option+Enter works.

Steps to Reproduce

1. Open Claude Code chat input
2. Try Shift+Enter → sends message instead of newline ❌
3. Try Ctrl+Enter → sends message instead of newline ❌
4. Try Cmd+Enter → sends message instead of newline ❌
5. Try Option+Enter → creates newline ✅

Expected Behavior

All modifier+Enter combinations should work for creating a newline in the chat input.

Actual Behavior

Only Option+Enter works. All other standard newline shortcuts send the message instead.

Environment

• macOS (darwin)
• Claude Code latest version
• This happened after Claude Code Instructions auto-update today
• Was working this morning (Shift+Enter worked fine)

Workaround

Use Option+Enter instead (works, but unexpected regression)

Impact

Users on Mac who relied on Shift+Enter for newlines now have a broken workflow.