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/controller.py

@@ -1,3 +1,4 @@
+from engine.effects.performance import get_monitor
 from engine.effects.registry import get_registry
 
 
@@ -16,6 +17,7 @@ def handle_effects_command(cmd: str) -> str:
         /effects <name> off - disable an effect
         /effects <name> intensity <0.0-1.0> - set intensity
         /effects reorder <name1>,<name2>,... - reorder pipeline
+        /effects stats - show performance statistics
     """
     parts = cmd.strip().split()
     if not parts or parts[0] != "/effects":
@@ -34,6 +36,9 @@ def handle_effects_command(cmd: str) -> str:
             result.append(f"Order: {chain.get_order()}")
         return "\n".join(result)
 
+    if parts[1] == "stats":
+        return _format_stats()
+
     if len(parts) < 3:
         return "Usage: /effects <name> on|off|intensity <value>"
 
@@ -72,6 +77,30 @@ def handle_effects_command(cmd: str) -> str:
     return f"Unknown action: {action}"
 
 
+def _format_stats() -> str:
+    monitor = get_monitor()
+    stats = monitor.get_stats()
+
+    if "error" in stats:
+        return stats["error"]
+
+    lines = ["Performance Stats:"]
+
+    pipeline = stats["pipeline"]
+    lines.append(
+        f"  Pipeline: avg={pipeline['avg_ms']:.2f}ms min={pipeline['min_ms']:.2f}ms max={pipeline['max_ms']:.2f}ms (over {stats['frame_count']} frames)"
+    )
+
+    if stats["effects"]:
+        lines.append("  Per-effect (avg ms):")
+        for name, effect_stats in stats["effects"].items():
+            lines.append(
+                f"    {name}: avg={effect_stats['avg_ms']:.2f}ms min={effect_stats['min_ms']:.2f}ms max={effect_stats['max_ms']:.2f}ms"
+            )
+
+    return "\n".join(lines)
+
+
 def show_effects_menu() -> str:
     """Generate effects menu text for display."""
     registry = get_registry()