fix: parse MCP result payloads and drop place idempotency_key

Typed result structs replace empty envelopes. Equity place sends
ref_id only so live additionalProperties:false schemas accept the call.

accounts/accounts_test.go

@@ -208,3 +208,17 @@ func TestPortfolio_rhntest(t *testing.T) {
 		t.Fatalf("buying power %s", got.BuyingPower)
 	}
 }
+
+func TestSearch_parsesResults(t *testing.T) {
+	t.Parallel()
+	c := accounts.New(client.Func(func(ctx context.Context, name string, args map[string]any) (json.RawMessage, error) {
+		return json.RawMessage(`{"results":[{"symbol":"AAPL","name":"Apple","instrument_id":"i1"}]}`), nil
+	}))
+	got, err := c.Search(context.Background(), accounts.SearchRequest{Query: "apple"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(got.Results) != 1 || got.Results[0].Symbol != "AAPL" || got.Results[0].InstrumentID != "i1" {
+		t.Fatalf("%+v", got)
+	}
+}