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

backend/app/domain/matching.py

@@ -0,0 +1,13 @@
+"""Fuzzy grounding: decide whether a search hit matches an LLM candidate."""
+
+from difflib import SequenceMatcher
+
+
+def normalize(text: str) -> str:
+    """Lowercase and strip decorations that vary across releases."""
+    return text.lower().strip()
+
+
+def title_similarity(candidate_title: str, catalog_title: str) -> float:
+    """Ratio in [0, 1] between a proposed title and a catalog title."""
+    return SequenceMatcher(None, normalize(candidate_title), normalize(catalog_title)).ratio()