fix(sensors): add inlet/outlet types to SensorStage

- Add DataType properties to SensorStage
- Fix MicSensor import issues (remove conflicting TYPE_CHECKING)
- Add numpy to main dependencies for type hints

engine/sensors/__init__.py

@@ -151,6 +151,7 @@ class SensorStage:
     """Pipeline stage wrapper for sensors.
 
     Provides sensor data to the pipeline context.
+    Sensors don't transform data - they inject sensor values into context.
     """
 
     def __init__(self, sensor: Sensor, name: str | None = None):
@@ -159,6 +160,22 @@ class SensorStage:
         self.category = "sensor"
         self.optional = True
 
+    @property
+    def stage_type(self) -> str:
+        return "sensor"
+
+    @property
+    def inlet_types(self) -> set:
+        from engine.pipeline.core import DataType
+
+        return {DataType.ANY}
+
+    @property
+    def outlet_types(self) -> set:
+        from engine.pipeline.core import DataType
+
+        return {DataType.ANY}
+
     @property
     def capabilities(self) -> set[str]:
         return {f"sensor.{self.name}"}