Add input_cost_trend / input_cost_series MCP tools (EIA diesel)

Real input price + WoW/YoY change + seasonal for diesel ($/gal). Formatters now
handle the item/label payload shape. Changelog updated.

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

tests/test_format.py

@@ -118,6 +118,19 @@ def test_fmt_price_trend_diesel_units():
     assert "$5.520/gal" in out   # 3-decimal $/gal formatting
 
 
+def test_fmt_input_cost_payload_shape():
+    # Input-cost payload uses item/label and has no geo.
+    payload = {"item": "diesel", "label": "retail diesel", "unit": "$/gal", "source": "EIA",
+               "trend": {"period": "2026-05-25", "value_cents": 552, "prev_cents": 560,
+                         "change_cents": -8, "change_pct": -1.4, "yoy_cents": 349,
+                         "yoy_change_cents": 203, "yoy_pct": 58.2, "seasonal": None,
+                         "recent_direction": "down", "baseline_years": 10, "points": 1680}}
+    out = fmt.fmt_price_trend(payload)
+    assert "diesel — retail diesel" in out   # item/label header, no geo segment
+    assert "$5.520/gal" in out
+    assert "+58.2%" in out                   # YoY surfaced
+
+
 def test_fmt_inputs_lime_table():
     payload = {
         "product": "lime", "count": 2,