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-5906-pce-ra.md

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+# LH 5906 PCE RA
+
+- **Vendor:** Latham Hi-Tech Seeds (independent family-owned, Alexander, IA)
+- **Brand:** Latham Hi-Tech Seeds
+- **Crop:** Corn
+- **Relative maturity:** 109 days
+- **Trait(s):** Powercore Enlist Corn
+- **Source:** https://www.lathamseeds.com/products/lh-5906-pce-ra/
+- **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)
+
+---
+
+_At 109 RM LH 5906 PCE RA is a medium stature PowerCore Enlist hybrid bringing fast dry down, outstanding stalk and root strength with low green snap risk to your farm. Consistent and girthy ears with very deep kernels, LH5906 PC ERA will find its best performance in and South of RM zone. This hybrid brings very good tolerance to Goss Bacterial Wilt, Gray leaf spot, fall stalk rot and is a Grain First / Silage Capable hybrid._
+
+---
+
+## Agronomic Characteristics
+
+- **Early Vigor:** 2.0
+- **Stalk Strength:** 1.0
+- **Root Strength:** 2.0
+- **Stay Green:** 2.0
+- **Drydown:** 2.0
+- **Test Weight:** 3.0
+- **Drought Tolerance:** 3.0
+- **Foliar Fungicide:** 2.0
+- **Corn-on-Corn:** 2.0
+- **Ear Height:** Medium
+- **Ear Type:** Flex
+
+## Disease Ratings
+
+- **Goss’s Wilt:** 2.0
+- **Northern Leaf Blight:** 4.0
+- **Anthracnose Stalk Rot:** 2.0
+- **Gray Leaf Spot:** 2.0