security: hash SHA-256 della query nell'audit log (niente contenuto in chiaro)

- query_hash (16 char) al posto di query[:80]
- verificato sul server: audit con query_hash, nessuna query in chiaro

gateway/main.py

@@ -337,7 +337,14 @@ async def search_memories(body: SearchIn, key: str = Depends(require_auth)) -> d
         }
         for h in hits
     ]
-    _audit(key, "search", query=body.query[:80], top_k=body.top_k, min_score=body.min_score, hits=len(results))
+    _audit(
+        key,
+        "search",
+        query_hash=hashlib.sha256(body.query.encode()).hexdigest()[:16],
+        top_k=body.top_k,
+        min_score=body.min_score,
+        hits=len(results),
+    )
     return {"results": results, "min_score": body.min_score, "total_hits": len(results)}