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-2025-9890.md

@@ -0,0 +1,39 @@
+# Corn yield trial — A.J. Geer (Monroe, IA, 2025)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2025
+- **Location:** Monroe, IA · Jasper County
+- **Cooperator:** A.J. Geer
+- **Company rep:** Jake Ekstrand
+- **Planted:** 4/14/2025
+- **Harvested:** 10/25/2025
+- **Previous crop:** Soybeans
+- **Row width:** 30
+- **Population:** 35,000 seeds/acre
+- **Tillage:** No-Till
+- **Irrigation:** Non-Irrigated
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2025/10/Corn-Geer-Monroe-IA.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | Renk | 8585 | TRE | 252.86 | 13.7 | 58.8 | 13.5 |
+| 2 | NuTech | 71B6 | PCE | 249.08 | 13.3 | 61.2 | 9.7 |
+| 3 | Renk | 889 | PCE | 246.37 | 12.6 | 59.6 | 7 |
+| 4 | NuTech | 71A7 | V | 245.67 | 13.1 | 62.5 | 6.3 |
+| 5 | ProHarvest | 83P48 | SSPRO | 245.53 | 13.5 | 60.8 | 6.1 |
+| 6 | NuTech | 73B2 | V | 244.96 | 13 | 59.8 | 5.6 |
+| 7 | NuTech | 69C7 | PCE | 244.1 | 12.9 | 61.8 | 4.7 |
+| 8 | ProHarvest | 84P41 | PCE | 241.44 | 14 | 58.3 | 2 |
+| 9 | ProHarvest | 83P66 | VT2PRIB | 240.29 | 13.3 | 60.4 | 0.9 |
+| 10 | Renk | RK825 | VT4P | 238.02 | 13.3 | 61.8 | -1.4 |
+| 11 | NuTech | 69F3 | V | 237.01 | 13.1 | 59.6 | -2.4 |
+| 12 | ProHarvest | 81P45 | TRERIB | 234.31 | 13.1 | 61 | -5.1 |
+| 13 | ProHarvest | 86P55 | TRERIB | 234.28 | 14 | 57.1 | -5.1 |
+| 14 | Renk | RK876 | VT2P | 231.18 | 14 | 58.9 | -8.2 |
+| 15 | Renk | RK800 | VT4PRO | 226.29 | 12.8 | 61.4 | -13.1 |
+| 16 | Renk | RK958 | VT2P | 219.15 | 13.2 | 59.8 | -20.3 |