Add fertilizer to input-cost tools (regional $/ton, USDA AgTransport)

input_cost_trend/input_cost_series now accept six fertilizers (urea, uan,
anhydrous, dap, map, potash) alongside diesel, with an optional `geo` region
(default Cornbelt). Real $/ton + MoM/YoY change + seasonal context.

- client: pass geo through; add input_cost_geographies
- server: expand VALID_INPUTS; geo param + docstrings
- format already unit-aware ($/ton) and geo-aware
- README tools table now lists the reference/trend + input-cost tools
- CHANGELOG: regional fertilizer input-cost release notes
- tests: fertilizer $/ton + region formatting

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

tests/test_format.py

@@ -131,6 +131,21 @@ def test_fmt_input_cost_payload_shape():
     assert "+58.2%" in out                   # YoY surfaced
 
 
+def test_fmt_input_cost_fertilizer_ton_and_region():
+    # Fertilizer payload carries item + geo (region) + $/ton.
+    payload = {"item": "urea", "geo": "Cornbelt", "label": "urea", "unit": "$/ton",
+               "source": "USDA AgTransport",
+               "trend": {"period": "2026-03-01", "value_cents": 69812, "prev_cents": 51812,
+                         "change_cents": 18000, "change_pct": 34.7, "yoy_cents": 45500,
+                         "yoy_change_cents": 24312, "yoy_pct": 53.4, "seasonal": None,
+                         "recent_direction": "up", "baseline_years": 10, "points": 39}}
+    out = fmt.fmt_price_trend(payload)
+    assert "urea — Cornbelt — urea" in out   # item, region, label all present
+    assert "$698.12/ton" in out
+    assert "USDA AgTransport" in out
+    assert "Mar 2026" in out                 # monthly period rendered as month
+
+
 def test_fmt_inputs_lime_table():
     payload = {
         "product": "lime", "count": 2,