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-l-0847-e3.md

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+# L 0847 E3
+
+- **Vendor:** Latham Hi-Tech Seeds (independent family-owned, Alexander, IA)
+- **Brand:** Latham Hi-Tech Seeds
+- **Crop:** Soybeans
+- **Maturity group:** 0.8
+- **Trait(s):** Enlist E3
+- **Source:** https://www.lathamseeds.com/products/l-0847-e3/
+- **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)
+
+---
+
+_Dual Phytophthora Root Rot genes and excellent Iron Deficiency Chlorosis tolerance help create a variety worthy of planting on all soil types. This Ironclad variety will not disappoint Latham customers in high or low yield environments. The excellent plant canopy and emergence score provide added piece of mind for early planting. Superior Sclerotinia White Mold tolerance provides added piece of mind._
+
+---
+
+## Agronomic Characteristics
+
+- **Relative Maturity:** 0.8
+- **Emergence:** 2.0
+- **Plant Height:** Medium
+- **Plant Type:** Medium Bushy
+- **Flower Color:** Purple
+- **Pubescence:** Light Tawny
+- **Pod Color:** Brown
+- **Hilum Color:** Brown
+
+## Disease Ratings
+
+- **SCN Resistance:** PI 88788
+- **Iron Chlorosis:** 1.5
+- **Stress Tolerance:** 2.0
+- **Phytophthora Root Rot:** 1K/3A, 2.5
+- **Brown Stem Rot:** 1.5
+- **White Mold:** 2.0
+- **Sudden Death:** 2.0