feat(pipeline): add self-documenting pipeline introspection

- Add --pipeline-diagram flag to generate mermaid diagrams
- Create engine/pipeline.py with PipelineIntrospector
- Outputs flowchart, sequence diagram, and camera state diagram
- Run with: python mainline.py --pipeline-diagram

engine/config.py

@@ -245,6 +245,9 @@ WEBSOCKET_PORT = _arg_int("--websocket-port", 8765)
 DEMO = "--demo" in sys.argv
 DEMO_EFFECT_DURATION = 5.0  # seconds per effect
 
+# ─── PIPELINE DIAGRAM ────────────────────────────────────
+PIPELINE_DIAGRAM = "--pipeline-diagram" in sys.argv
+
 
 def set_font_selection(font_path=None, font_index=None):
     """Set runtime primary font selection."""