chore(pipeline): improve pipeline architecture

- Add capability-based dependency resolution with prefix matching
- Add EffectPluginStage with sensor binding support
- Add CameraStage adapter for camera integration
- Add DisplayStage adapter for display integration
- Add Pipeline metrics collection
- Add deprecation notices to legacy modules
- Update app.py with pipeline integration

engine/display/__init__.py

@@ -26,8 +26,20 @@ class Display(Protocol):
     - clear(): Clear the display
     - cleanup(): Shutdown the display
 
+    Optional methods for keyboard input:
+    - is_quit_requested(): Returns True if user pressed Ctrl+C/Q or Escape
+    - clear_quit_request(): Clears the quit request flag
+
     The reuse flag allows attaching to an existing display instance
     rather than creating a new window/connection.
+
+    Keyboard input support by backend:
+    - terminal: No native input (relies on signal handler for Ctrl+C)
+    - pygame: Supports Ctrl+C, Ctrl+Q, Escape for graceful shutdown
+    - websocket: No native input (relies on signal handler for Ctrl+C)
+    - sixel: No native input (relies on signal handler for Ctrl+C)
+    - null: No native input
+    - kitty: Supports Ctrl+C, Ctrl+Q, Escape (via pygame-like handling)
     """
 
     width: int