Add basis_movement/basis_detail tools; make history + latest fully filterable

New MCP tools:
- basis_movement: aggregated basis trend, one headline line per crop. The cheap
  "how is basis moving overall" view; optional commodity/source/delivery/days.
- basis_detail: per-(elevator, crop, delivery) basis first→last drill-down.

Both do the aggregation MCP-side and return compact markdown to keep token
burn low, so a client can call the cheap aggregate first and drill in only when
needed.

Flexibility/parity changes:
- price_history: commodity is now optional (spans all crops); groups by
  (source, commodity, delivery); surfaces basis first→last in the summary and
  adds a futures column to the raw table.
- latest_prices: expose the `kind` filter (grain/fertilizer) that the API and
  client already supported.
- client.history(): commodity optional.

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

tests/test_client.py

@@ -71,6 +71,25 @@ def test_get_drops_none_params(monkeypatch):
     assert captured["params"] == {"commodity": "corn"}
 
 
+def test_history_without_commodity_drops_param(monkeypatch):
+    client = _reload_client(monkeypatch)
+    captured = {}
+
+    class FakeResp:
+        status_code = 200
+        text = ""
+        def json(self): return {"rows": []}
+
+    def fake_get(url, params=None, timeout=None, headers=None):
+        captured["params"] = dict(params or {})
+        return FakeResp()
+
+    monkeypatch.setattr(client.httpx, "get", fake_get)
+    client.history(days=14)
+    # commodity/source_id/delivery all None → only days survives
+    assert captured["params"] == {"days": 14}
+
+
 def test_get_raises_on_non_200(monkeypatch):
     client = _reload_client(monkeypatch)