refactor: remove verification field from responses and update related documentation

src/storage.py

@@ -222,15 +222,14 @@ class HistoryDB:
     def _parse_response_payload(self, response_json: str | None, result: str | None) -> dict[str, Any]:
         fallback_return = str(result or "").strip()
         if not response_json:
-            return {"return": fallback_return, "data": None, "verification": None}
+            return {"return": fallback_return, "data": None}
         try:
             payload = json.loads(response_json)
             if isinstance(payload, dict):
                 return {
                     "return": str(payload.get("return") or fallback_return),
                     "data": payload.get("data"),
-                    "verification": payload.get("verification"),
                 }
         except Exception:
             pass
-        return {"return": fallback_return, "data": None, "verification": None}
+        return {"return": fallback_return, "data": None}