- Add isCtrlA/C/E/K/O/P/T/U/W helper functions that check both raw and Kitty formats
- Add isAltBackspace helper function
- Refactor editor.ts, input.ts, select-list.ts to use helper functions
- Refactor custom-editor.ts, session-selector.ts, user-message-selector.ts
- Add CHANGELOG entry for the Shift+Enter fix