Add 4 independent seed brands: Latham + Stine + 1st Choice + Burrus (+623 varieties) (#17)

Co-authored-by: claude <claude@jpaul.io>
Co-committed-by: claude <claude@jpaul.io>

corpus/latham/latham-lh-3151-rr.md

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+# LH 3151 RR
+
+- **Vendor:** Latham Hi-Tech Seeds (independent family-owned, Alexander, IA)
+- **Brand:** Latham Hi-Tech Seeds
+- **Crop:** Corn
+- **Relative maturity:** 81 days
+- **Trait(s):** RR-Corn
+- **Source:** https://www.lathamseeds.com/products/lh-3151-rr/
+- **Rating scale:** 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.
+- **Service area:** Latham dealer network — Upper Midwest (IA/MN/WI/IL/ND/SD/NE)
+
+---
+
+_A versatile hybrid with excellent seedling vigor, LH 3151 RR is built for the north. It features strong stalk and roots, as well as versatility across soils and yield environments. This hybrid handles stress well. It produces girthy ears and high test weight when planted in its zone and north._
+
+---
+
+## Agronomic Characteristics
+
+- **Flowering for Maturity:** Equal
+- **Early Vigor:** 1.5
+- **Stalk Strength:** 2.0
+- **Root Strength:** 2.0
+- **Stay Green:** 3.5
+- **Drydown:** 2.0
+- **Test Weight:** 2.0
+- **Drought Tolerance:** 2.0
+- **Foliar Fungicide:** 2.0
+- **Herbicide Sensitivity:** None Known
+- **Suggested Population:** 30-36
+- **Corn-on-Corn:** 3.0
+- **Ear Height:** Medium
+- **Ear Type:** Flex
+- **Number of Kernel Rows:** 16-18
+- **Cob Color:** Red
+- **Husk Cover:** Medium
+- **Shank Length:** Medium
+- **Leaf Angle:** Semi-Upright
+
+## Disease Ratings
+
+- **Goss’s Wilt:** 3.0
+- **Common Rust:** 2.0
+- **Northern Leaf Blight:** 2.0
+- **Anthracnose Stalk Rot:** 2.0
+- **Gray Leaf Spot:** 2.0