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-soybeans-2025-r4.md

@@ -0,0 +1,52 @@
+# Soybean yield trial — University of Illinois VT, Region 4, IL 2025
+
+- **Publisher:** University of Illinois Variety Testing (independent cross-vendor trial)
+- **Crop:** Soybean
+- **State:** IL
+- **Year:** 2025
+- **Region:** Region 4
+- **Rotation:** corn following soybean
+- **Cooperator / host:** Emmerick Farms
+- **County:** Fayette
+- **Sites:** St Peter, Belleville
+- **Soil type:** Parke silt loam
+- **Tillage:** Vertical Till
+- **Planted:** 2025-06-02
+- **Harvested:** 2025-11-03
+- **Source XLSX:** https://vt.cropsci.illinois.edu/wp-content/uploads/2025/12/2025-Region-4.xlsx
+- **Index page:** https://vt.cropsci.illinois.edu/soybeans/
+
+---
+
+## Results (ranked by regional yield)
+
+| Rank | Brand | Product | Traits | Yield | Protein | Oil |
+|---|---|---|---|---|---|---|
+| 1 | Confluence Genetics | BH35A233 | HT:CV ST:BS | 69.32 | 34.73 | 20.23 |
+| 2 | Xitavo | XO 3855E | HT:EN ST:Be | 69.29 | 35.8 | 19.8 |
+| 3 | Xitavo | XO 3555E | HT:EN ST:Be | 69.08 | 33.4 | 21.22 |
+| 4 | Hoffman | H38E25 | HT:EN ST:B | 68.37 | 33.83 | 20.69 |
+| 5 | Hoffman | H35E26 | HT:EN ST:B | 65.87 | 33.37 | 21.22 |
+| 6 | DONMARIO | DM33E55 | HT:EN ST:BS | 65.2 | 33.98 | 21.57 |
+| 7 | Confluence Genetics | BH36U203 | HT:CV ST:BS | 62.01 | 39.33 | 17.4 |
+| 8 | Confluence Genetics | BH37Q218 | HT:CV ST:BS | 61.97 | 37.95 | 18.32 |
+| 9 | DONMARIO | DM40F45S | HT:RF ST:BS | 60.84 | 34 | 20.1 |
+| 10 | Confluence Genetics | C38H052S | HT:STS ST:BS | 59.6 | 36.93 | 19.22 |
+| 11 | Confluence Genetics | BH39A232 | HT:CV ST:BS | 58.87 | 34.45 | 20.27 |
+| 12 | Xitavo | XO 4255E | HT:EN ST:Be | 58.85 | 35.6 | 19.52 |
+| 13 | DONMARIO | DM36E94 | HT:EN ST:BS | 58.83 | 33.65 | 21.37 |
+| 14 | Burrus | 3908F | HT:RF ST:BS | 58.57 | 33.98 | 20.72 |
+| 15 | DONMARIO | DM38E54 | HT:EN ST:BS | 58.27 | 34.25 | 20.85 |
+| 16 | DONMARIO | DM37F85 | HT:RF ST:BS | 57.7 | 34.47 | 19.48 |
+| 17 | Hoffman | H43E25 | HT:EN ST:B | 56.77 | 33.98 | 20.73 |
+| 18 | Confluence Genetics | BH39A150 | HT:CV ST:BS | 55.88 | 28.8 | 16.72 |
+| 19 | Confluence Genetics | N35D950S | HT:STS ST:BS | 55.72 | 38.65 | 18.17 |
+| 20 | Burrus | 4353E | HT:EN ST:BS | 55.51 | 28.47 | 17.15 |
+| 21 | Xitavo | XO 4056E | HT:EN ST:Be | 55.36 | 29.03 | 17.08 |
+| 22 | Lakeview Farms | LVF4085 | HT:CV ST:B | 54.53 | 27.58 | 17.47 |
+| 23 | Baird Seed | Illini 4300N | HT:CV ST:BS | 54.52 | 34.35 | 21.23 |
+| 24 | Hoffman | H41E26 | HT:EN ST:B | 54.28 | 33.73 | 20.83 |
+| 25 | Confluence Genetics | BH38F550 | HT:CV ST:BS | 53.82 | 37.47 | 18.45 |
+| 26 | Lakeview Farms | LVF3973 | HT:CV ST:B | 52.41 | 34.85 | 20.43 |
+| 27 | Confluence Genetics | BX39C784 | HT:CV ST:BS | 50.23 | 35.97 | 19.25 |
+| 28 | Confluence Genetics | C37H051S | HT:STS ST:BS | 48.15 | 36.57 | 18.27 |