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-corn-2025-9918.md

@@ -0,0 +1,43 @@
+# Corn yield trial — Jacob Robinson (Aledo, IL, 2025)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2025
+- **Location:** Aledo, IL · Mercer County
+- **Cooperator:** Jacob Robinson
+- **Company rep:** Ronn Dillavou
+- **Planted:** 5/8/2025
+- **Harvested:** 10/8/2025
+- **Previous crop:** Soybeans
+- **Row width:** 30"
+- **Population:** 34,500 seeds/acre
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2025/10/Corn-Robinson-Aleda-IL.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | Pioneer | P11616PCE | PCE | 262.72 | 14.3 | 61.0 | 28.1 |
+| 2 | Pioneer | P1742Q | Qrome | 260.89 | 16.7 | 57.8 | 26.3 |
+| 3 | ProHarvest | 84P78 | TRE RIB | 259.68 | 12.4 | 60.1 | 25.0 |
+| 4 | Golden Harvest | G13M31-AA | AA | 255.85 | 16.6 | 58.3 | 21.2 |
+| 5 | ProHarvest | 82P96 | PCE | 254.78 | 13.9 | 58.1 | 20.1 |
+| 6 | Pioneer | P13777PCE | PCE | 254.62 | 15.0 | 58.8 | 20.0 |
+| 7 | ProHarvest | 80P75PCE | PCE | 238.33 | 13.2 | 57.5 | 3.7 |
+| 8 | Golden Harvest | G12U11-AA | AA | 234.47 | 14.5 | 60.6 | -0.2 |
+| 9 | Wyffels | W7759RIB | SSPRO | 234.45 | 13.5 | 59.1 | -0.2 |
+| 10 | Dekalb | DKC112-12RIB | TRE RIB | 234.42 | 13.2 | 60.3 | -0.2 |
+| 11 | Dekalb | DKC114-99RIB | VT4P RIB | 232.21 | 13.8 | 61.3 | -2.4 |
+| 12 | Golden Harvest | G15U34-V | V | 232.09 | 16.5 | 58.6 | -2.5 |
+| 13 | AgriGold | A642-32VT2PRIB | VT2P RIB | 229.87 | 13.5 | 61.1 | -4.8 |
+| 14 | Wyffels | W7945RIB | TRE RIB | 226.95 | 12.9 | 59.7 | -7.7 |
+| 15 | Wyffels | W7876RIB | VT2P RIB | 226.14 | 12.2 | 66.0 | -8.5 |
+| 16 | Wyffels | W7485RIB | TRE RIB | 224.21 | 12.4 | 60.4 | -10.4 |
+| 17 | AgriGold | A644-64VT2RIB | VT2P RIB | 221.45 | 13.4 | 59.3 | -13.2 |
+| 18 | Dekalb | DKC66-06RIB | TRE RIB | 218.96 | 14.7 | 59.5 | -15.7 |
+| 19 | Wyffels | W7499RIB | SSPRO | 218.92 | 13.1 | 59.0 | -15.7 |
+| 20 | Dekalb | DKC68-35RIB | VT2P RIB | 218.77 | 14.9 | 61.5 | -15.9 |
+| 21 | Golden Harvest | G14B32-DV | DV | 217.95 | 14.1 | 58.0 | -16.7 |
+| 22 | ProHarvest | 86P55 | TRE RIB | 204.31 | 13.7 | 55.6 | -30.3 |