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-6445-vt2-pro-rib.md

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+# LH 6445 VT2 PRO RIB
+
+- **Vendor:** Latham Hi-Tech Seeds (independent family-owned, Alexander, IA)
+- **Brand:** Latham Hi-Tech Seeds
+- **Crop:** Corn
+- **Relative maturity:** 114 days
+- **Trait(s):** VT2 PRO RIB
+- **Source:** https://www.lathamseeds.com/products/lh-6445-vt2-pro-rib/
+- **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)
+
+---
+
+_Expected to be the new king of our later offerings, LH 6445 VT2 PRO RIB shows stable performance from east to west across Latham Country. LH 6445 VT2 PRO RIB responds to high management and moves north very well. Note its strong ear-flex coupled with girth, as well as its thick, deep kernels. LH 6445 VT2 PRO RIB is a Grain First / Silage Capable hybrid._
+
+---
+
+## Agronomic Characteristics
+
+- **Early Vigor:** 2.0
+- **Stalk Strength:** 2.0
+- **Root Strength:** 2.0
+- **Stay Green:** 2.0
+- **Drydown:** 3.0
+- **Test Weight:** 2.0
+- **Drought Tolerance:** 1.5
+- **Foliar Fungicide:** 2.0
+- **Corn-on-Corn:** 2.0
+- **Ear Height:** Medium HIgh
+- **Ear Type:** Flex
+
+## Disease Ratings
+
+- **Goss’s Wilt:** 2.0
+- **Northern Leaf Blight:** 2.0
+- **Anthracnose Stalk Rot:** ASR
+- **Gray Leaf Spot:** 2.0