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

engine/display/backends/pygame.py

@@ -37,6 +37,7 @@ class PygameDisplay:
         self._screen = None
         self._font = None
         self._resized = False
+        self._quit_requested = False
 
     def _get_font_path(self) -> str | None:
         """Get font path for rendering."""
@@ -130,8 +131,6 @@ class PygameDisplay:
         self._initialized = True
 
     def show(self, buffer: list[str]) -> None:
-        import sys
-
         if not self._initialized or not self._pygame:
             return
 
@@ -139,7 +138,15 @@ class PygameDisplay:
 
         for event in self._pygame.event.get():
             if event.type == self._pygame.QUIT:
-                sys.exit(0)
+                self._quit_requested = True
+            elif event.type == self._pygame.KEYDOWN:
+                if event.key in (self._pygame.K_ESCAPE, self._pygame.K_c):
+                    if event.key == self._pygame.K_c and not (
+                        event.mod & self._pygame.KMOD_LCTRL
+                        or event.mod & self._pygame.KMOD_RCTRL
+                    ):
+                        continue
+                    self._quit_requested = True
             elif event.type == self._pygame.VIDEORESIZE:
                 self.window_width = event.w
                 self.window_height = event.h
@@ -210,3 +217,20 @@ class PygameDisplay:
     def reset_state(cls) -> None:
         """Reset pygame state - useful for testing."""
         cls._pygame_initialized = False
+
+    def is_quit_requested(self) -> bool:
+        """Check if user requested quit (Ctrl+C, Ctrl+Q, or Escape).
+
+        Returns True if the user pressed Ctrl+C, Ctrl+Q, or Escape.
+        The main loop should check this and raise KeyboardInterrupt.
+        """
+        return self._quit_requested
+
+    def clear_quit_request(self) -> bool:
+        """Clear the quit request flag after handling.
+
+        Returns the previous quit request state.
+        """
+        was_requested = self._quit_requested
+        self._quit_requested = False
+        return was_requested