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/mic.py

@@ -1,6 +1,10 @@
 """
 Microphone input monitor — standalone, no internal dependencies.
 Gracefully degrades if sounddevice/numpy are unavailable.
+
+.. deprecated::
+    For pipeline integration, use :class:`engine.sensors.mic.MicSensor` instead.
+    MicMonitor is still used as the backend for MicSensor.
 """
 
 import atexit
@@ -20,7 +24,11 @@ from engine.events import MicLevelEvent
 
 
 class MicMonitor:
-    """Background mic stream that exposes current RMS dB level."""
+    """Background mic stream that exposes current RMS dB level.
+
+    .. deprecated::
+        For pipeline integration, use :class:`engine.sensors.mic.MicSensor` instead.
+    """
 
     def __init__(self, threshold_db=50):
         self.threshold_db = threshold_db