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

tests/test_effects.py

@@ -282,3 +282,52 @@ class TestEffectsExports:
 
         for name in effects_module.__all__:
             getattr(effects_module, name)
+
+
+class TestPerformanceMonitor:
+    def test_empty_stats(self):
+        from engine.effects.performance import PerformanceMonitor
+
+        monitor = PerformanceMonitor()
+        stats = monitor.get_stats()
+        assert "error" in stats
+
+    def test_record_and_retrieve(self):
+        from engine.effects.performance import PerformanceMonitor
+
+        monitor = PerformanceMonitor()
+        monitor.start_frame(1)
+        monitor.record_effect("test_effect", 1.5, 100, 150)
+        monitor.end_frame(1, 2.0)
+
+        stats = monitor.get_stats()
+        assert "error" not in stats
+        assert stats["frame_count"] == 1
+        assert "test_effect" in stats["effects"]
+
+    def test_multiple_frames(self):
+        from engine.effects.performance import PerformanceMonitor
+
+        monitor = PerformanceMonitor(max_frames=3)
+        for i in range(5):
+            monitor.start_frame(i)
+            monitor.record_effect("effect1", 1.0, 100, 100)
+            monitor.record_effect("effect2", 0.5, 100, 100)
+            monitor.end_frame(i, 1.5)
+
+        stats = monitor.get_stats()
+        assert stats["frame_count"] == 3
+        assert "effect1" in stats["effects"]
+        assert "effect2" in stats["effects"]
+
+    def test_reset(self):
+        from engine.effects.performance import PerformanceMonitor
+
+        monitor = PerformanceMonitor()
+        monitor.start_frame(1)
+        monitor.record_effect("test", 1.0, 100, 100)
+        monitor.end_frame(1, 1.0)
+
+        monitor.reset()
+        stats = monitor.get_stats()
+        assert "error" in stats