refactor: phase 4 - event-driven architecture foundation

- Add EventBus class with pub/sub messaging (thread-safe)
- Add emitter Protocol classes (EventEmitter, Startable, Stoppable)
- Add event emission to NtfyPoller (NtfyMessageEvent)
- Add event emission to MicMonitor (MicLevelEvent)
- Update StreamController to publish stream start/end events
- Add comprehensive tests for eventbus and emitters modules

engine/controller.py

@@ -3,6 +3,8 @@ Stream controller - manages input sources and orchestrates the render stream.
 """
 
 from engine.config import Config, get_config
+from engine.eventbus import EventBus
+from engine.events import EventType, StreamEvent
 from engine.mic import MicMonitor
 from engine.ntfy import NtfyPoller
 from engine.scroll import stream
@@ -11,8 +13,9 @@ from engine.scroll import stream
 class StreamController:
     """Controls the stream lifecycle - initializes sources and runs the stream."""
 
-    def __init__(self, config: Config | None = None):
+    def __init__(self, config: Config | None = None, event_bus: EventBus | None = None):
         self.config = config or get_config()
+        self.event_bus = event_bus
         self.mic: MicMonitor | None = None
         self.ntfy: NtfyPoller | None = None
 
@@ -38,8 +41,27 @@ class StreamController:
         """Run the stream with initialized sources."""
         if self.mic is None or self.ntfy is None:
             self.initialize_sources()
+
+        if self.event_bus:
+            self.event_bus.publish(
+                EventType.STREAM_START,
+                StreamEvent(
+                    event_type=EventType.STREAM_START,
+                    headline_count=len(items),
+                ),
+            )
+
         stream(items, self.ntfy, self.mic)
 
+        if self.event_bus:
+            self.event_bus.publish(
+                EventType.STREAM_END,
+                StreamEvent(
+                    event_type=EventType.STREAM_END,
+                    headline_count=len(items),
+                ),
+            )
+
     def cleanup(self) -> None:
         """Clean up resources."""
         if self.mic: