feat(effects): add performance monitoring to effect pipeline

- Add PerformanceMonitor to collect per-effect timings
- Track effect duration (ms), buffer chars in/out per frame
- Store last 60 frames in ring buffer
- Add /effects stats NTFY command to view performance data
- Add tests for performance monitoring system

engine/effects/__init__.py

@@ -8,6 +8,7 @@ from engine.effects.legacy import (
     noise,
     vis_trunc,
 )
+from engine.effects.performance import PerformanceMonitor, get_monitor, set_monitor
 from engine.effects.registry import EffectRegistry, get_registry, set_registry
 from engine.effects.types import EffectConfig, EffectContext, PipelineConfig
 
@@ -27,6 +28,9 @@ __all__ = [
     "get_registry",
     "set_registry",
     "get_effect_chain",
+    "get_monitor",
+    "set_monitor",
+    "PerformanceMonitor",
     "handle_effects_command",
     "show_effects_menu",
     "fade_line",