Add university-extension trials: Illinois VT + Iowa ICPT + Ohio OCPT (+123 cross-vendor trial docs) (#19)

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

corpus/illinois_vt_trials/ilvt-corn-2024-urbana-cfc.md

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+# Corn yield trial — University of Illinois VT, Urbana CFC, IL 2024
+
+- **Publisher:** University of Illinois Variety Testing (independent cross-vendor trial)
+- **Crop:** Corn
+- **State:** IL
+- **Year:** 2024
+- **Region:** Urbana CFC
+- **Rotation:** corn following corn
+- **Previous crop:** corn
+- **Cooperator / host:** Darin Joos
+- **County:** Chamapign
+- **Sites:** Urbana
+- **Soil type:** Drummer silty clay loam
+- **Tillage:** None
+- **Planted:** 2024-05-20
+- **Harvested:** 2024-10-18
+- **Source XLSX:** https://vt.cropsci.illinois.edu/wp-content/uploads/2024/11/Urbana-CFC-Table-2024.xlsx
+- **Index page:** https://vt.cropsci.illinois.edu/corn/
+
+---
+
+## Results (ranked by regional yield)
+
+| Rank | Brand | Product | Traits | Yield | Moisture | Lodging | Maturity |
+|---|---|---|---|---|---|---|---|
+| 1 | Prairie | 6755 | - | 190.876 | 16.64 | 0.33 | 110 |
+| 2 | Prairie | 6854 | - | 179.6544 | 14.33 | 1 | 110 |
+| 3 | Prairie | 7184 | - | 176.0747 | 16.85 | 1 | 112 |
+| 4 | Prairie | 8864 | - | 170.8097 | 18.23 | 1 | 114 |
+| 5 | Prairie | 8683 | - | 164.3276 | 20.2 | 0.67 | 115 |
+| 6 | Prairie | 9703 | - | 158.9303 | 18.57 | 1 | 116 |