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/ohio_ocpt_trials/ocpt-soybeans-2024-south-late.md

@@ -0,0 +1,47 @@
+# Soybean yield trial — late maturity, OH (South, 2024)
+
+- **Publisher:** Ohio Crop Performance Test (independent third-party, all brands)
+- **Vendor:** The Ohio State University (CFAES extension)
+- **Crop:** Soybean
+- **Year:** 2024
+- **Region:** South
+- **Site:** late maturity
+- **Source table:** TABLE 8: The 2024 Ohio Soybean Performance Trials, South Region - Late Varieties (RM 3.7-4.4)
+- **Cooperator / sites:** S1=Preble Co.; S2=Clinton Co.
+- **Source PDF:** https://ohiocroptest.cfaes.osu.edu/soy2024/2024OCJwithproteinandoil.pdf
+- **Note:** © OSU on the report; explicit no-endorsement clause; public CFAES extension publication; attribute Ohio Corn/Soybean Performance Test, OSU CFAES.
+
+---
+
+## Results (by yield rank)
+
+| Rank | Brand | Hybrid/Variety | Traits | RM | Yield S1 | Yield S2 | Yield |
+|---|---|---|---|---|---|---|---|
+| 1 | Seed Genetics Direct | ET-4738E3 | EN | 3.8 | 87.3 | 84.4 | 85.9 |
+| 2 | Dyna-Gro Seed | S38EN75 | EN | 3.8 | 83.1 | 86 | 84.6 |
+| 3 | Ebberts Field Seeds | E3760 E3 | EN | 3.7 | 82 | 84.9 | 83.5 |
+| 4 | NK Seeds | NK40-P5E3 | EN | 4 | 77.4 | 86.5 | 82 |
+| 5 | Axis | 3835E | EN | 3.8 | 78.4 | 85.1 | 81.8 |
+| 6 | Asgrow | AG39XF3 | XF | 3.9 | 81.9 | 80.7 | 81.3 |
+| 7 | Golden Harvest | GH3774E3 | EN | 3.7 | 74.9 | 86.8 | 80.9 |
+| 8 | Seed Consultants, Inc. | SC7375ETM | EN | 3.7 | 77.5 | 84.1 | 80.8 |
+| 9 | Benson Hill | BH39A232 | CV | 3.9 | 78.4 | 82.2 | 80.3 |
+| 10 | Seed Consultants, Inc. | SC7385ETM | EN | 3.8 | 72.9 | 87.5 | 80.2 |
+| 11 | Benson Hill | BX37C755 | CV | 3.7 | 77.5 | 81.7 | 79.6 |
+| 12 | Golden Harvest | GH3994E3 | EN | 3.9 | 72.8 | 85.5 | 79.2 |
+| 13 | NK Seeds | NK39-J2E3 | EN | 3.9 | 72.8 | 85.3 | 79.1 |
+| 14 | NK Seeds | NK37-C1E3 | EN | 3.7 | 78.3 | 79.5 | 78.9 |
+| 15 | Seed Genetics Direct | ET-4739E3 | EN | 3.9 | 73.2 | 78.7 | 76 |
+| 16 | Xitavo | XO 3855E | EN | 3.8 | 73.5 | 78.4 | 76 |
+| 17 | DonMario | DM38E54 | EN | 3.8 | 75.2 | 75.4 | 75.3 |
+| 18 | Seed Genetics Direct | ET-3739E3S | EN | 3.9 | 74 | 76.6 | 75.3 |
+| 19 | Benson Hill | BX37Q467 | CV | 3.7 | 73.7 | 76.5 | 75.1 |
+| 20 | Xitavo | XO 3795E | EN | 3.7 | 70.5 | 78.4 | 74.5 |
+| 21 | Asgrow | AG43XF2 | XF | 4.3 | 71.6 | 75.7 | 73.7 |
+| 22 | Seed Genetics Direct | ET-4743E3S | EN | 4.3 | 77.5 | 69.7 | 73.6 |
+| 23 | Dyna-Gro Seed | S40EN54 | EN | 4 | 70.8 | 75.3 | 73.1 |
+| 24 | Benson Hill | BH37Q218 | CV | 3.7 | 72.7 | 71.4 | 72.1 |
+| 25 | Benson Hill | BH37U205 | CV | 3.8 | 68.5 | 69.6 | 69.1 |
+| 26 | Benson Hill | C38H052S | CV | 3.8 | 66.8 | 68.4 | 67.6 |
+| 27 | Xitavo | XO 4255E | EN | 4.2 | 59.3 | 71.7 | 65.5 |
+| 28 | Seed Genetics Direct | ET-4744E3S | EN | 4.4 | 62.7 | 67.5 | 65.1 |