Add university-extension variety trials: Illinois VT + Iowa ICPT + Ohio OCPT (+123 trial docs)

Independent third-party performance data — land-grant programs that test every
entered brand side-by-side with replication + LSD stats. This is the legitimate
way to get Pioneer / DEKALB / Brevant / Channel performance the corpus can't
scrape directly (data_type=trial, results[] shape; falls through the trial
chunker).

- illinois_vt_trials (30 docs, 1,392 rows) — U of Illinois VT. Per-region XLSX
  (openpyxl), corn + soy + WHEAT, 2024+2025. Rich per-site agronomic metadata;
  corn-following-corn vs -soybean kept distinct.
- iowa_icpt_trials (24 docs, 674 rows) — Iowa State ICPT. ASP.NET GridView
  (viewstate postback for year/district), corn + soy by district x season.
- ohio_ocpt_trials (69 docs, 4,647 rows) — OSU/CFAES OCPT. Report PDF
  (pdfplumber; per-site column groups split by header Yield-token count +
  x-coord footnote bucketing), corn + soy per site, 2024+2025.

91 distinct seed brands across the three; majors confirmed present in the
independent rankings: DEKALB 395, Golden Harvest 249, Channel 241, NK 212,
Xitavo 135, LG 103, Pioneer 88, Asgrow 59. (A brand only appears where it
ENTERED a given program — e.g. Brevant not in Iowa, DEKALB/Channel not in
Illinois — true negatives, not parse gaps.)

- rag/chunk.py: gated `include_region` on _render_gh_plot_chunk; the 3 university
  sources route through it so the region/district is in the embedded chunk +
  labeled "variety trial (cross-vendor, independent third-party)". Existing plot
  sources (gh/lg/agrigold/proharvest) unchanged.
- requirements.txt: openpyxl (Illinois XLSX; scrape-time only).
- sources.json + README/CLAUDE/lessons: registered + attributed; lessons
  trial-data + Pioneer entries updated (Pioneer/DEKALB performance now available
  indirectly via these trials).

Validation: all 123 chunk via rag.chunk.chunks_from_trial (0 errors), 0
out-of-range yields, 0 dup keys. Public land-grant data; attribution recorded in
each tos_note. CI rebuilds the index from the committed corpus.

corpus/illinois_vt_trials/ilvt-corn-2025-r1.md

@@ -0,0 +1,46 @@
+# Corn yield trial — University of Illinois VT, Region 1, IL 2025
+
+- **Publisher:** University of Illinois Variety Testing (independent cross-vendor trial)
+- **Crop:** Corn
+- **State:** IL
+- **Year:** 2025
+- **Region:** Region 1
+- **Rotation:** corn following soybean
+- **Cooperator / host:** Highland C.C.
+- **County:** Stephenson
+- **Sites:** Freeport, DeKalb
+- **Soil type:** Fayette silt loam
+- **Tillage:** Field cultivator
+- **Planted:** 2025-05-12
+- **Harvested:** 2025-10-21
+- **Source XLSX:** https://vt.cropsci.illinois.edu/wp-content/uploads/2025/11/Region-1-Corn-Table-2025.xlsx
+- **Index page:** https://vt.cropsci.illinois.edu/corn/
+
+---
+
+## Results (ranked by regional yield)
+
+| Rank | Brand | Product | Traits | Yield | Moisture | Lodging | Maturity |
+|---|---|---|---|---|---|---|---|
+| 1 | Cornelius | C7164 | IST:L | 272.78 | 16.72 | 1.67 | 111 |
+| 2 | Prairie | 6436 | - | 272.35 | 16.82 | 1.17 | 111 |
+| 3 | Prairie | 4556 | - | 270.9 | 15.7 | 1.17 | 104 |
+| 4 | Prairie | 6251 | - | 270.81 | 15.62 | 0.5 | 111 |
+| 5 | Cornelius | C6618 | IST:L | 270.43 | 15.83 | 0.67 | 106 |
+| 6 | Prairie | 7241 | - | 267.18 | 16.93 | 0.33 | 112 |
+| 7 | Prairie | 3054 | - | 266.64 | 14.85 | 2.67 | 103 |
+| 8 | Cornelius | C7399 | IST:L | 262.83 | 17.25 | 1.83 | 113 |
+| 9 | Prairie | 7445 | - | 262.75 | 17.62 | 1.5 | 113 |
+| 10 | Viking | Blue River | 75-07 | - | 262.73 | 16.12 | 1.5 | 107 |
+| 11 | Cornelius | C6900 | IST:L | 262.33 | 16.57 | 1 | 109 |
+| 12 | Cornelius | C6523 | IST:L | 262.31 | 14.72 | 3 | 105 |
+| 13 | Cornelius | C7026 | IST:L | 261.85 | 16.45 | 1.67 | 110 |
+| 14 | Prairie | 2235 | - | 259.68 | 15 | 2.17 | 105 |
+| 15 | Prairie | 7265 | - | 256.96 | 16.33 | 2.33 | 112 |
+| 16 | Prairie | 6854 | - | 256.2 | 14.77 | 0.17 | 110 |
+| 17 | Viking | Blue River | 76-11 | - | 253.92 | 14.95 | 0.83 | 111 |
+| 18 | Cornelius | C7235 | IST:L | 252.81 | 19.2 | 1.17 | 112 |
+| 19 | Prairie | 2311 | - | 246.88 | 15.08 | 1.83 | 106 |
+| 20 | Prairie | 8786 | - | 246.44 | 15.18 | 0.33 | 115 |
+| 21 | Viking | Blue River | 49-05 | - | 239.94 | 14.43 | 2.33 | 105 |
+| 22 | Prairie | 6755 | - | 237.31 | 16.23 | 0.83 | 110 |