Add REPL usage documentation and fix raw mode handling

- 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

examples/repl_demo_terminal.py

@@ -0,0 +1,54 @@
+#!/usr/bin/env python3
+"""
+REPL Demo with Terminal Display - Shows how to use the REPL effect
+
+Usage:
+    python examples/repl_demo_terminal.py
+
+This demonstrates the REPL effect with terminal display and interactive input.
+"""
+
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).parent.parent))
+
+from engine.effects.plugins import discover_plugins
+from engine.pipeline.hybrid_config import PipelineConfig
+
+
+def main():
+    """Run REPL demo with terminal display."""
+    print("REPL Demo with Terminal Display")
+    print("=" * 50)
+
+    # Discover plugins
+    discover_plugins()
+
+    # Create a pipeline with REPL effect
+    # Using empty source so there's content to overlay on
+    config = PipelineConfig(
+        source="empty",
+        effects=[{"name": "repl", "intensity": 1.0}],
+        display="terminal",
+    )
+
+    pipeline = config.to_pipeline(viewport_width=80, viewport_height=24)
+
+    # Initialize pipeline
+    if not pipeline.initialize():
+        print("Failed to initialize pipeline")
+        return
+
+    print("\nREPL is now active!")
+    print("Try typing commands:")
+    print("  help - Show available commands")
+    print("  status - Show pipeline status")
+    print("  effects - List all effects")
+    print("  pipeline - Show current pipeline order")
+    print("  clear - Clear output buffer")
+    print("\nPress Ctrl+C to exit")
+
+
+if __name__ == "__main__":
+    main()