fix: Bug fixes and improvements

- fix(demo-lfo-effects): Fix math.sin() usage (was angle.__sin__())
- feat(pipeline): Add set_effect_intensity() method for runtime effect control
  - Allows changing effect intensity during pipeline execution
  - Returns False if effect not found or intensity out of range
  - Used by LFO modulation demo

The demo-lfo-effects.py script now works correctly with proper
math.sin() usage and the new set_effect_intensity() method provides
a clean API for runtime effect intensity control.

engine/pipeline/controller.py

@@ -984,6 +984,35 @@ class Pipeline:
         """Get historical frame times for sparklines/charts."""
         return [f.total_ms for f in self._frame_metrics]
 
+    def set_effect_intensity(self, effect_name: str, intensity: float) -> bool:
+        """Set the intensity of an effect in the pipeline.
+
+        Args:
+            effect_name: Name of the effect to modify
+            intensity: New intensity value (0.0 to 1.0)
+
+        Returns:
+            True if successful, False if effect not found or not an effect stage
+        """
+        if not 0.0 <= intensity <= 1.0:
+            return False
+
+        stage = self._stages.get(effect_name)
+        if not stage:
+            return False
+
+        # Check if this is an EffectPluginStage
+        from engine.pipeline.adapters.effect_plugin import EffectPluginStage
+
+        if isinstance(stage, EffectPluginStage):
+            # Access the underlying effect plugin
+            effect = stage._effect
+            if hasattr(effect, "config"):
+                effect.config.intensity = intensity
+                return True
+
+        return False
+
 
 class PipelineRunner:
     """High-level pipeline runner with animation support."""

scripts/demo-lfo-effects.py

@@ -14,6 +14,7 @@ Effects modulated:
 The LFO uses a sine wave to oscillate intensity between 0.0 and 1.0.
 """
 
+import math
 import sys
 import time
 from dataclasses import dataclass
@@ -64,7 +65,7 @@ class LFOEffectDemo:
             angle = (
                 (elapsed * effect_cfg.frequency + effect_cfg.phase_offset) * 2 * 3.14159
             )
-            lfo_value = 0.5 + 0.5 * (angle.__sin__())
+            lfo_value = 0.5 + 0.5 * math.sin(angle)
 
             # Scale to intensity range
             intensity = effect_cfg.min_intensity + lfo_value * (