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>

ag_bids_mcp/client.py

@@ -80,12 +80,16 @@ 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_trend(item: str, years: int = 10, geo: str | None = None) -> dict:
+    return _get("/api/data/input-cost-trend", item=item, years=years, geo=geo)
 
 
-def input_cost_series(item: str) -> dict:
-    return _get("/api/data/input-cost-series", item=item)
+def input_cost_series(item: str, geo: str | None = None) -> dict:
+    return _get("/api/data/input-cost-series", item=item, geo=geo)
+
+
+def input_cost_geographies(item: str) -> dict:
+    return _get("/api/data/input-cost-geographies", item=item)
 
 
 def futures(commodity: str, delivery: str | None = None) -> dict: