Add ProHarvest Seeds: 119 varieties + 161 cross-vendor plot reports

ProHarvest Seeds (independent Corn Belt brand, proharvestseeds.com) exposes
a public, no-auth WordPress REST API — cleaner ingestion than the HTML-only
independents. Two new sources:

- `proharvest` (variety identity, 119 row-crop varieties: 70 corn / 47 soy /
  2 wheat). Enumerated via /wp/v2/seed (seed-type taxonomy), agronomics
  parsed from each /seed/<slug>/ detail page into structured
  characteristics_groups so the ratings actually embed. Mixed scale: disease
  1-9 numeric (9=best, no flip), agronomic/general qualitative, soil HR/R.

- `proharvest_plots` (trials, data_type=trial, 161 plots, 2024+2025). Per-
  cooperator harvest reports via the custom /wp-json/proharvest/v1/plots?y=
  endpoint + PDF table extraction. Many are cross-vendor head-to-head
  (ProHarvest/Apex vs Pioneer/DEKALB/Becks/Channel/Wyffels). Handles ruled
  tables, unruled tables (text fallback; soy drops the Test-Wt column → 4 vs
  5 numerics), and off-template third-party reports (sanity-gated to verbatim
  so junk rows never ship). Image-only PDFs skipped + counted.

- rag/chunk.py: route proharvest_plots through the shared cross-vendor plot
  renderer (structured) / verbatim body (raw_text fallback).
- sources.json + lessons.md (rating-scales, trial-data).
- README/CLAUDE.md corpus inventory brought current (it had drifted: bayer
  931 not 475; ebberts/lg/agrigold were unlisted). New totals: 1,645 variety
  + 6,787 trial records.

robots.txt permissive (only search + /dealer-* disallowed); no ToS
automation clause. CI rebuilds the index from the committed corpus.

corpus/proharvest_plots/phpr-soybeans-2024-9643.md

@@ -0,0 +1,36 @@
+# Soybean yield trial — ROMAR LLC. (Cairo, NE, 2024)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Soybean
+- **Year:** 2024
+- **Location:** Cairo, NE · Hall County
+- **Cooperator:** ROMAR LLC.
+- **Company rep:** Derald Watson
+- **Planted:** 5/18/2024
+- **Harvested:** 10/3/2024
+- **Previous crop:** Corn
+- **Row width:** 30"
+- **Tillage:** Min-Till
+- **Irrigation:** Irrigated
+- **Fungicide:** Yes
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2024/11/Soy-Roy-John-Stoltenberg-Cairo-NE-68824.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | Pioneer | P30A75E | E3 | 81.11 | 7.9 | 56.6 | 6.1 |
+| 2 | Pioneer | P31Z03E | E3 | 80.5 | 8.7 | 56.2 | 5.5 |
+| 3 | Pioneer | P26Z78E | E3 | 79.97 | 7.8 | 56.8 | 4.9 |
+| 4 | Apex | AE2940S | E3 | 79.36 | 8.4 | 56.5 | 4.3 |
+| 5 | Pioneer | P27Z41E | E3 | 77.06 | 8.1 | 57.2 | 2.0 |
+| 6 | Pioneer | P33Z17E | E3 | 76.48 | 8.8 | 56.9 | 1.5 |
+| 7 | Pioneer | P28Z30E | E3 | 75.99 | 7.8 | 56.8 | 1.0 |
+| 8 | ProHarvest | 31E37 | E3 | 75.04 | 8.1 | 56.5 | 0.0 |
+| 9 | Apex | AE2940S | E3 | 72.2 | 7.9 | 56.8 | -2.8 |
+| 10 | Apex | AE2940S | E3 | 71.85 | 8.9 | 56.7 | -3.2 |
+| 11 | Pioneer | P34A98E | E3 | 70.33 | 8.5 | 56.7 | -4.7 |
+| 12 | Apex | AE3330S | E3 | 69.84 | 8.9 | 55.8 | -5.2 |
+| 13 | ProHarvest | 3548E | E3 | 65.48 | 8.9 | 56.8 | -9.5 |