feat: add pipeline introspection demo mode

- Add PipelineIntrospectionSource that renders live ASCII DAG with metrics
- Add PipelineMetricsSensor exposing pipeline performance as sensor values
- Add PipelineIntrospectionDemo controller with 3-phase animation:
  - Phase 1: Toggle effects one at a time (3s each)
  - Phase 2: LFO drives intensity default→max→min→default
  - Phase 3: All effects with shared LFO (infinite loop)
- Add pipeline-inspect preset
- Add get_frame_times() to Pipeline for sparkline data
- Add tests for new components
- Update mise.toml with pipeline-inspect preset task

engine/pipeline_sources/__init__.py

@@ -0,0 +1,7 @@
+"""
+Data source implementations for the pipeline architecture.
+"""
+
+from engine.pipeline_sources.pipeline_introspection import PipelineIntrospectionSource
+
+__all__ = ["PipelineIntrospectionSource"]