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-2025-9872.md

@@ -0,0 +1,39 @@
+# Corn yield trial — Berenda Ag Solutions (Earl Park, IN, 2025)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2025
+- **Location:** Earl Park, IN · Benton County
+- **Cooperator:** Berenda Ag Solutions
+- **Company rep:** Doug Hanson
+- **Planted:** 5/12/2025
+- **Harvested:** 10/17/2025
+- **Previous crop:** Soybeans
+- **Row width:** 20"
+- **Population:** 34,000 seeds/acre
+- **Tillage:** Conventional
+- **Fungicide:** No
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2025/10/Corn-Berenda-Ag-Earl-Park-IN.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | ProHarvest | 81P45 | TRE RIB | 269.62 | 15.8 | - | 16.5 |
+| 2 | ProHarvest | 84P78 | TRE RIB | 267.65 | 17.9 | - | 14.5 |
+| 3 | ProHarvest | 79P54 | SSPRO | 267.59 | 16.0 | - | 14.5 |
+| 4 | Channel | 214-78 | DGVT2P RIB | 263.29 | 16.7 | - | 10.2 |
+| 5 | ProHarvest | 82P96 | PCE | 260.91 | 16.8 | - | 7.8 |
+| 6 | ProHarvest | 80P75 | PCE | 259.23 | 14.4 | - | 6.1 |
+| 7 | ProHarvest | 79P87 | SS RIB | 254.43 | 18.0 | - | 1.3 |
+| 8 | ProHarvest | 86P55 | TRE RIB | 251.18 | 16.6 | - | -1.9 |
+| 9 | ProHarvest | 79P87 | SS RIB | 250.73 | 14.4 | - | -2.4 |
+| 10 | ProHarvest | 84P41 | PCE | 250.22 | 17.6 | - | -2.9 |
+| 11 | ProHarvest | 79P87 | SS RIB | 250.02 | 14.4 | - | -3.1 |
+| 12 | ProHarvest | 79P87 | SS RIB | 249.9 | 15.4 | - | -3.2 |
+| 13 | ProHarvest | 83P48 | SSPRO | 246.11 | 15.5 | - | -7.0 |
+| 14 | ProHarvest | 83P66 | VT2P RIB | 240.81 | 14.4 | - | -12.3 |
+| 15 | ProHarvest | 85P58 | VT2P RIB | 236.79 | 18.7 | - | -16.3 |
+| 16 | Channel | 213-23 | VT2P RIB | 231.42 | 15.5 | - | -21.7 |