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-2024-9547.md

@@ -0,0 +1,23 @@
+# Corn yield trial — Synergy Seeds Herscher 2 (Herscher, IL, 2024)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2024
+- **Location:** Herscher, IL · Kankakee County
+- **Cooperator:** Synergy Seeds Herscher 2
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2024/11/Corn-Synergy-Herscher-IL-60941.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 25 | Dekalb | 64-22 | VT2P 4 574 1800 13.4 248.5 25 $ | 9.0 | - | - | 94.07 |
+| 26 | Agrigold | 644-64 | VT2P 4 574 1820 14.6 247.8 26 $ | 9.0 | - | - | 91.19 |
+| 27 | Wyffels | 6505 | Trec 4 574 1740 12.6 242.5 28 $ | 9.0 | - | - | 69.82 |
+| 28 | ProHarvest | 83P66 | VT2P 4 574 1760 14.0 241.3 29 $ | 9.0 | - | - | 65.25 |
+| 29 | Wyffels | 6479 | SSPro 4 574 1820 15.9 244.0 27 $ | 9.0 | - | - | 65.12 |
+| 30 | Wyffels | 7945 | Trec 4 574 1760 14.5 239.9 30 $ | 9.0 | - | - | 59.64 |
+| 31 | Dekalb | 66-06 | Trec 4 574 1800 16.5 239.6 31 $ | 9.0 | - | - | 40.52 |
+| 32 | ProHarvest | 77P60 | SS 4 574 1680 13.0 233.0 32 $ | 9.0 | - | - | 32.09 |