refactor: remove legacy controller.py and MicMonitor

- Delete engine/controller.py (StreamController - deprecated)
- Delete engine/mic.py (MicMonitor - deprecated)
- Delete tests/test_controller.py (was testing removed legacy code)
- Delete tests/test_mic.py (was testing removed legacy code)
- Update tests/test_emitters.py to test MicSensor instead of MicMonitor
- Clean up pipeline.py introspector to remove StreamController reference
- Update AGENTS.md to reflect architecture changes

engine/pipeline.py

@@ -319,18 +319,7 @@ class PipelineIntrospector:
         )
 
     def introspect_scroll(self) -> None:
-        """Introspect scroll engine."""
-        self.add_node(
-            PipelineNode(
-                name="StreamController",
-                module="engine.controller",
-                class_name="StreamController",
-                description="Main render loop orchestrator",
-                inputs=["items", "ntfy_poller", "mic_monitor", "display"],
-                outputs=["buffer"],
-            )
-        )
-
+        """Introspect scroll engine (legacy - replaced by pipeline architecture)."""
         self.add_node(
             PipelineNode(
                 name="render_ticker_zone",