- Add _quit_requested flag to TerminalDisplay
- Add request_quit() method to TerminalDisplay
- Handle 'ctrl_c' key in REPL input loops in both pipeline_runner.py and main.py
- When Ctrl+C is pressed, request_quit() is called which sets the flag
- The main loop checks is_quit_requested() and raises KeyboardInterrupt
- Fix raw mode enabling to not duplicate with UI border mode
- Add REPL_USAGE.md with comprehensive guide
- Add examples/repl_demo_terminal.py example script
- Detect REPL effect in pipeline and enable interactive mode
- Enable raw terminal mode for REPL input capture
- Add keyboard input loop for REPL commands
- Add _handle_pipeline_mutation() function for pipeline control
