Changelog: source geo + many more elevator locations

Document the per-source geo on /api/data/sources + list_sources, and the new
Heritage Cooperative (23 locations), expanded Mercer Landmark (16, with two
source renames), and Bambauer Pemberton sources.

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

CHANGELOG.md

@@ -3,6 +3,39 @@
 Notes for clients/agents that consume the ag-bids MCP tools and the underlying
 `ag-monitor` `/api/data/*` HTTP API. Newest first.
 
+## 2026-05-30 — Source geo + many more locations
+
+### Per-source geo (API + MCP)
+
+- **`GET /api/data/sources`** now returns location geo on every source:
+  `city, state, zip, county, latitude, longitude` (any may be `null`). The
+  AgriCharts-fed elevators carry exact coordinates; smaller sites carry
+  city/state/zip.
+- **MCP `list_sources`** gained a **Location** column (`City, ST ZIP`).
+  `source_health` is unchanged in shape.
+- Sources that are national or non-physical (CBOT futures, USDA AMS, DTN
+  fertilizer, hedge-to-arrive / "Direct" bid buckets) legitimately have `null`
+  geo. ~43 of ~51 sources are geo-tagged.
+
+### Many more elevator locations
+
+These flow through every data tool/endpoint automatically (`latest`, `history`,
+`best`, `basis_movement`/`basis_detail`, `sources`, `deliveries`). No tool
+signatures changed — just far more sources, all named `"<Co-op> — <Location>"`:
+
+- **Heritage Cooperative** — new co-op, **23 central/eastern-Ohio locations**
+  (corn/soy/wheat).
+- **Mercer Landmark** — expanded from 2 to **all ~16 locations**. Note: the two
+  old source names were renamed for continuity — `"Mercer Landmark — St Henry"`
+  → `"Mercer Landmark — MPS St Henry"`, `"Mercer Landmark — Minster"` →
+  `"Mercer Landmark — Heartland Minster"`.
+- **Bambauer** — now both locations incl. **Pemberton**
+  (`"Bambauer — Jackson Center / New Knoxville"`, `"Bambauer — Pemberton"`);
+  the old `"Bambauer Jackson Center / New Knoxville, OH"` source was renamed to
+  the first of those.
+
+If you cache source names, refresh them — several changed and many were added.
+
 ## 2026-05-29 — Futures price + change tool
 
 ### New MCP tool