feat: scaffold FastAPI backend with ports-and-adapters layout

backend/app/pipeline/orchestrator.py

@@ -0,0 +1,11 @@
+"""Pipeline orchestrator: the five stages composed and timed, nothing else."""
+
+from app.ports.protocols import MusicCatalog, Recommender
+
+
+class DiscoveryPipeline:
+    """Session context -> intent+candidates -> grounding -> rerank -> action."""
+
+    def __init__(self, catalog: MusicCatalog, recommender: Recommender) -> None:
+        self._catalog = catalog
+        self._recommender = recommender