Location params on best_local_bid / latest_prices (zip / GPS + radius)

Thread zip/lat/lng/radius_miles through the client and both tools; friendly
guard for the zip-XOR-gps rule. Formatters surface distance, the searched
center, and the nearest-source hint when nothing is in range.

- client: best()/latest() take zip/lat/lng/radius_miles
- server: location params + docstrings (note Ohio-concentrated coverage)
- format: distance column + center/nearest rendering
- README + CHANGELOG + advisor prompt library updated
- tests: location formatting cases

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

tests/test_format.py

@@ -35,6 +35,60 @@ def test_fmt_best_no_winner():
     assert "wheat" in out
 
 
+def test_fmt_best_with_location_shows_distance():
+    payload = {
+        "commodity": "corn", "today": "2026-05-20",
+        "center": {"lat": 40.78, "lng": -83.81, "zip": "45810", "source": "zip"},
+        "radius_miles": 50.0,
+        "best": {
+            "source_name": "Heritage Cooperative — Ada", "city": "Ada", "state": "OH",
+            "delivery": "May 2026", "bid_cents": 486, "basis_cents": 20,
+            "futures_contract": "ZCN26", "distance_miles": 2.3,
+            "fetched_at": "2026-05-20T15:00:00+00:00",
+        },
+    }
+    out = fmt.fmt_best("corn", payload)
+    assert "(Ada, OH)" in out
+    assert "2.3 mi" in out
+    assert "within 50 mi of ZIP 45810" in out
+
+
+def test_fmt_best_out_of_range_reports_nearest():
+    payload = {
+        "commodity": "corn", "today": "2026-05-20", "best": None,
+        "center": {"lat": 42.0, "lng": -93.6, "zip": "50010", "source": "zip"},
+        "radius_miles": 50.0,
+        "nearest": {"source_name": "Heritage Cooperative — Ada", "city": "Ada",
+                    "state": "OH", "distance_miles": 513.5},
+    }
+    out = fmt.fmt_best("corn", payload)
+    assert "No current-month corn bids within 50 mi of ZIP 50010" in out
+    assert "Nearest tracked elevator" in out
+    assert "513.5 mi" in out
+
+
+def test_fmt_latest_with_location_adds_distance_column():
+    payload = {
+        "center": {"lat": 40.78, "lng": -83.81, "zip": "45810", "source": "zip"},
+        "radius_miles": 50.0,
+        "rows": [
+            {"source_name": "Heritage Cooperative — Ada", "commodity": "corn",
+             "display_name": "Corn", "commodity_kind": "grain", "delivery": "May 2026",
+             "bid_cents": 486, "basis_cents": 20, "futures_contract": "ZCN26",
+             "distance_miles": 2.3, "fetched_at": "2026-05-20T15:00:00+00:00"},
+        ],
+    }
+    out = fmt.fmt_latest(payload)
+    assert "Distance" in out and "2.3 mi" in out
+    assert "within 50 mi of ZIP 45810" in out
+
+
+def test_fmt_latest_location_no_rows():
+    payload = {"center": {"zip": "50010", "source": "zip"}, "radius_miles": 50.0, "rows": []}
+    out = fmt.fmt_latest(payload)
+    assert "No sources within 50 mi of ZIP 50010" in out
+
+
 def test_fmt_futures_with_changes():
     payload = {
         "commodity": "corn", "delivery": "Jul 2026", "contract": "ZCN26",