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>

README.md

@@ -75,7 +75,7 @@ auto-updates it every 5 minutes.
 
 | Tool | Returns |
 |---|---|
-| `best_local_bid(commodity)` | Where to sell `corn`, `soy`, or `wheat` for this month's delivery — markdown one-liner + table |
+| `best_local_bid(commodity, zip?, lat?, lng?, radius_miles?)` | Where to sell `corn`/`soy`/`wheat` for this month's delivery. Optional location (zip **or** lat/lng + `radius_miles`, default 50) restricts to nearby elevators and shows distance; out-of-range returns the nearest-source hint |
 | `futures_quote(commodity, delivery?)` | CBOT futures price + change since open + change on the day. With a delivery month it resolves the listed contract; without it, the continuous nearby |
 | `current_lime_price()` | Latest lime quotes across all manual-entry sources |
 | `current_input_price(product?)` | MAP / Potash / Lime — all three or one (local DTN dealer feed) |
@@ -83,7 +83,7 @@ auto-updates it every 5 minutes.
 | `price_series(commodity, geo?, start_year?, end_year?)` | Raw monthly price-received series for charting |
 | `input_cost_trend(item, geo?, years?)` | Real input cost + change. `item` = `diesel` (U.S. `$/gal`, weekly, EIA) or a fertilizer `$/ton` (`urea`/`uan`/`anhydrous`/`dap`/`map`/`potash`, monthly, USDA AgTransport); `geo` selects the fertilizer region (default `Cornbelt`) |
 | `input_cost_series(item, geo?)` | Raw historical series for an input cost (diesel `$/gal` or fertilizer `$/ton`, region-selectable) |
-| `latest_prices(commodity?, source?, delivery?, kind?)` | Live snapshot table; every filter optional (`kind` = `grain`/`fertilizer`) |
+| `latest_prices(commodity?, source?, delivery?, kind?, zip?, lat?, lng?, radius_miles?)` | Live snapshot table; every filter optional (`kind` = `grain`/`fertilizer`). Location filter (zip **or** lat/lng + `radius_miles`) keeps nearby sources, nearest-first, with distance |
 | `price_history(commodity?, source?, delivery?, days?)` | Time series per (elevator, crop, delivery); **every filter optional** — omit `commodity` to span all crops. Shows bid + basis trend + futures |
 | `basis_movement(commodity?, source?, delivery?, days?)` | Aggregated basis trend, one headline line per crop (the cheap overview) |
 | `basis_detail(commodity?, source?, delivery?, days?)` | Per-(elevator, crop, delivery) basis first→last drill-down |