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>

ag_bids_mcp/client.py

@@ -80,6 +80,14 @@ def price_series(commodity: str, geo: str = "US",
                 start_year=start_year, end_year=end_year)
 
 
+def input_cost_trend(item: str, years: int = 10) -> dict:
+    return _get("/api/data/input-cost-trend", item=item, years=years)
+
+
+def input_cost_series(item: str) -> dict:
+    return _get("/api/data/input-cost-series", item=item)
+
+
 def futures(commodity: str, delivery: str | None = None) -> dict:
     return _get("/api/data/futures", commodity=commodity, delivery=delivery)