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

mise.toml

@@ -54,7 +54,7 @@ run-pipeline-firehose = { run = "uv run mainline.py --pipeline --pipeline-preset
 # =====================
 
 run-preset-demo = { run = "uv run mainline.py --preset demo --display pygame", depends = ["sync-all"] }
-run-preset-pipeline = { run = "uv run mainline.py --preset pipeline --display pygame", depends = ["sync-all"] }
+run-preset-pipeline-inspect = { run = "uv run mainline.py --preset pipeline-inspect --display terminal", depends = ["sync-all"] }
 
 # =====================
 # Command & Control