Add futures_quote tool: CBOT price + change since open + on day

New futures_quote(commodity, delivery?) tool wraps the new /api/data/futures
endpoint: reports latest price, today's session open, prior settle, and both
moves (since open and on the day). With a delivery month it resolves the listed
contract; without it, the continuous nearby. Adds client.futures(), fmt_futures(),
tests, and a CHANGELOG entry.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_client.py

@@ -71,6 +71,29 @@ def test_get_drops_none_params(monkeypatch):
     assert captured["params"] == {"commodity": "corn"}
 
 
+def test_futures_endpoint_params(monkeypatch):
+    client = _reload_client(monkeypatch)
+    captured = {}
+
+    class FakeResp:
+        status_code = 200
+        text = ""
+        def json(self): return {"quote": None}
+
+    def fake_get(url, params=None, timeout=None, headers=None):
+        captured["url"] = url
+        captured["params"] = dict(params or {})
+        return FakeResp()
+
+    monkeypatch.setattr(client.httpx, "get", fake_get)
+    client.futures(commodity="corn", delivery="Jul 2026")
+    assert captured["url"].endswith("/api/data/futures")
+    assert captured["params"] == {"commodity": "corn", "delivery": "Jul 2026"}
+    # delivery omitted → dropped
+    client.futures(commodity="corn")
+    assert captured["params"] == {"commodity": "corn"}
+
+
 def test_history_without_commodity_drops_param(monkeypatch):
     client = _reload_client(monkeypatch)
     captured = {}