Add 4 independent seed brands: Latham, Stine, 1st Choice, Burrus (+623 varieties)

Four independent regional brands across IA/IN/IL (variety-identity sources,
each parsed into structured characteristics_groups so ratings embed):

- latham (264: 155 corn + 109 soy) — Latham Hi-Tech Seeds, Alexander IA.
  WordPress REST enum (/wp-json/wp/v2/varieties) + /products/<slug>/ detail
  HTML. Scale 1-9 LOWER=better (reversed, like NK/AgriPro).
- stine (217: 58 corn + 159 soy) — Stine Seed, Adel IA (largest US
  independent). sitemap enum + /{crop}/traits/<slug>/<code>/ detail HTML.
  Corn 1-9 (9=best); soy qualitative.
- first_choice (78: 52 corn + 22 soy + 4 wheat) — 1st Choice Seeds,
  Rushville IN (employee-owned). Per-crop sitemap -> detail HTML. Scale
  0-10 higher=better. ~40 older corn pages thin at source; wheat
  identity-only.
- burrus (64: 38 corn + 26 soy) — Burrus Seed, Arenzville IL. Seedware
  JSON API. Scale 1-10 (10=best). Brands Burrus/Power Plus/DONMARIO.
  robots ai-train=no + named-bot blocks; operator opted in, scraper uses a
  non-blacklisted UA + honors Crawl-delay 10.

All 623 validated through rag.chunk.chunks_from_variety (0 errors; 6
identity-only pages from source gaps). No chunk.py change needed (identity
sources auto-route to chunks_from_variety).

Docs:
- sources.json: 4 entries + Hoegemeyer added to _excluded_sources. The
  Corteva ToU (shared across pioneer.com / hoegemeyer.com / therightseed.com
  / corteva.com + the Vylor spinoff) bans scrapers + competitive use, so the
  whole Corteva family is one excluded ToU domain.
- docs_mcp/lessons.md: rating-scales updated with all 4 directions +
  an explicit cross-vendor warning (Latham 1=best vs Stine/Burrus higher=best
  — never compare raw numbers without _scale_direction).
- README + CLAUDE corpus inventory: now 2,268 variety + 6,787 trial records.

CI rebuilds the index from the committed corpus.

corpus/latham/latham-lh-4500-cnv.json

@@ -0,0 +1,107 @@
+{
+  "source": "latham",
+  "source_key": "latham-lh-4500-cnv",
+  "vendor": "Latham Hi-Tech Seeds",
+  "brand": "Latham Hi-Tech Seeds",
+  "product_name": "LH 4500 CNV",
+  "product_id": "LH 4500 CNV",
+  "crop": "corn",
+  "release_year": "2025",
+  "relative_maturity": 95,
+  "maturity_group": null,
+  "wheat_class": null,
+  "trait_stack": [
+    "CNV"
+  ],
+  "trait_descriptions": [],
+  "positioning_statement": "This medium-tall conventional hybrid offering at 95 days brings a strong multiyear data package with outstanding disease tolerance, large flex ears and very deep kernels. Youll find the best performance on medium and lighter soil types. LH 4500 is widely adapted from east to West and brings very good stress tolerance to your farm. LH 4500 is a Grain First / Silage Capable hybrid.",
+  "strengths": [],
+  "characteristics_groups": [
+    {
+      "label": "AGRONOMIC CHARACTERISTICS",
+      "items": [
+        {
+          "characteristic": "Early Vigor",
+          "value": "2.0"
+        },
+        {
+          "characteristic": "Stalk Strength",
+          "value": "3.0"
+        },
+        {
+          "characteristic": "Root Strength",
+          "value": "2.0"
+        },
+        {
+          "characteristic": "Stay Green",
+          "value": "2.0"
+        },
+        {
+          "characteristic": "Drydown",
+          "value": "3.0"
+        },
+        {
+          "characteristic": "Test Weight",
+          "value": "3.0"
+        },
+        {
+          "characteristic": "Drought Tolerance",
+          "value": "2.0"
+        },
+        {
+          "characteristic": "Foliar Fungicide",
+          "value": "2.0"
+        },
+        {
+          "characteristic": "Corn-on-Corn",
+          "value": "2.0"
+        },
+        {
+          "characteristic": "Ear Height",
+          "value": "Medium HIgh"
+        },
+        {
+          "characteristic": "Ear Type",
+          "value": "Flex"
+        }
+      ]
+    },
+    {
+      "label": "DISEASE RATINGS",
+      "items": [
+        {
+          "characteristic": "Goss’s Wilt",
+          "value": "1.5"
+        },
+        {
+          "characteristic": "Northern Leaf Blight",
+          "value": "2.0"
+        },
+        {
+          "characteristic": "Anthracnose Stalk Rot",
+          "value": "2.5"
+        },
+        {
+          "characteristic": "Gray Leaf Spot",
+          "value": "2.0"
+        }
+      ]
+    }
+  ],
+  "_scale_direction": "numeric ratings ~1-9 where LOWER = BETTER (1 = best / most tolerant / most resistant); confirmed by cross-referencing Product Overview prose vs values (top-rated stalks/roots cluster 1.0-1.5, weak traits 3.0-3.5, none approach 9). Categorical values pass through verbatim (SCN source 'PI 88788', Phytophthora 'Rps 1k', Anthracnose 'ASR', 'Medium Tall', 'Flex'). NA/blank = not rated.",
+  "regional_recommendations": [
+    {
+      "product_list_name": "Latham dealer network (Upper Midwest — IA/MN/WI/IL/ND/SD/NE)",
+      "agronomist": null,
+      "agronomist_email": null,
+      "variant_id": null
+    }
+  ],
+  "image_url": null,
+  "source_urls": [
+    "https://www.lathamseeds.com/products/lh-4500-cnv/"
+  ],
+  "sitemap_last_modified": null,
+  "fetched_at": "2026-06-05T01:45:20.384505+00:00",
+  "scraper_version": "0.1.0"
+}