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-2025-9892.md

@@ -0,0 +1,37 @@
+# Corn yield trial — Nolan Good (Baring, MO, 2025)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2025
+- **Location:** Baring, MO · Knox County
+- **Cooperator:** Nolan Good
+- **Company rep:** Jake Ekstrand
+- **Planted:** 5/10/2025
+- **Harvested:** 10/24/2025
+- **Previous crop:** Soybeans
+- **Row width:** 30
+- **Population:** 32,000 seeds/acre
+- **Tillage:** Conventional
+- **Irrigation:** Non-Irrigated
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2025/10/Corn-Good-Baring-MO.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | ProHarvest | 83P66 | CONV | 287.19 | 14.3 | 59.6 | 17 |
+| 2 | ProHarvest | 84P78 | CONV | 278.6 | 13.4 | 60.6 | 8.4 |
+| 3 | ProHarvest | 83P66 | VT2PRIB | 275.35 | 15 | 59.6 | 5.2 |
+| 4 | ProHarvest | 81P19 | VT4PRIB | 274.54 | 14.8 | 60.7 | 4.4 |
+| 5 | ProHarvest | 84P41 | PCE | 274.18 | 14.5 | 59.6 | 4 |
+| 6 | ProHarvest | 86P55 | TRERIB | 271.76 | 15.3 | 56.8 | 1.6 |
+| 7 | ProHarvest | 85P58 | VT2PRIB | 269.87 | 13 | 62.9 | -0.3 |
+| 8 | ProHarvest | 85P13 | CONV | 269.26 | 14.1 | 58.4 | -0.9 |
+| 9 | ProHarvest | 80P75 | CONV | 266.53 | 13.6 | 59.3 | -3.6 |
+| 10 | ProHarvest | 81P20 | CONV | 265.48 | 14.7 | 57.6 | -4.7 |
+| 11 | ProHarvest | 80P75 | CONV | 264.22 | 14 | 58.7 | -5.9 |
+| 12 | ProHarvest | 81P45 | TRERIB | 263.63 | 14.3 | 61 | -6.5 |
+| 13 | ProHarvest | 82P96 | PCE | 263.05 | 14.2 | 59.4 | -7.1 |
+| 14 | ProHarvest | 86P55 | TRERIB | 258.65 | 16.2 | 58 | -11.5 |