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-1383-xf.md

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+# L 1383 XF
+
+- **Vendor:** Latham Hi-Tech Seeds (independent family-owned, Alexander, IA)
+- **Brand:** Latham Hi-Tech Seeds
+- **Crop:** Soybeans
+- **Maturity group:** 1.3
+- **Trait(s):** XtendFlex
+- **Source:** https://www.lathamseeds.com/products/l-1383-xf/
+- **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)
+
+---
+
+_L 1383 XF is a 1.3 maturity Ironclad XtendFlex product that features SCN protection from PI 88788, the Rps3-a gene for Phytophthora and full resistance to Brown Stem Rot. It also has very good scores for Iron Chlorosis, White Mold and Stress tolerance. One parent of L 1383 X is L 0982 R2 which combined with the good height and Stress tolerance help make this soybean an excellent choice for those tougher fields all across Latham Country._
+
+---
+
+## Agronomic Characteristics
+
+- **Relative Maturity:** 1.3
+- **Emergence:** 1.5
+- **Plant Height:** Medium+
+- **Plant Type:** Medium
+- **Flower Color:** Purple
+- **Pubescence:** Light Tawny
+- **Pod Color:** Brown
+- **Hilum Color:** Black
+
+## Disease Ratings
+
+- **SCN Resistance:** F, 2.2
+- **Iron Chlorosis:** 2.0
+- **Stress Tolerance:** 1.8
+- **Phytophthora Root Rot:** 3a, 1.9
+- **Brown Stem Rot:** 1.0
+- **White Mold:** 2.2
+- **Sudden Death:** 2.8