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-2025-9832.md

@@ -0,0 +1,43 @@
+# Corn yield trial — Isu Farm (Lexington, IL, 2025)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2025
+- **Location:** Lexington, IL · Mclean County
+- **Cooperator:** Isu Farm
+- **Company rep:** Eric Yoder
+- **Planted:** 4/28/2025
+- **Harvested:** 9/30/2025
+- **Previous crop:** Soybeans
+- **Row width:** 30
+- **Population:** 35,000 seeds/acre
+- **Tillage:** No-Till
+- **Irrigation:** Non-Irrigated
+- **Fungicide:** Yes
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2025/10/Corn-ISU-Farm-Lexington-IL-min.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | ProHarvest | 86P55 | TRERIB | 296.7 | 21 | 53.6 | 34.4 |
+| 2 | ProHarvest | 85P58 | VT2PRIB | 284.85 | 17.7 | 59.5 | 22.6 |
+| 3 | ProHarvest | 83P66 | VT2PRIB | 283.86 | 20 | 55.9 | 21.6 |
+| 4 | ProHarvest | 84P78 | TRERIB | 282.53 | 18.7 | 56.9 | 20.2 |
+| 5 | ProHarvest | 81P45 | TRERIB | 273.41 | 19.8 | 55.5 | 11.1 |
+| 6 | ProHarvest | 83P48 | SSPRO | 270.41 | 18.5 | 58.8 | 8.1 |
+| 7 | ProHarvest | 80P75 | PCE | 268.92 | 16.4 | 55.8 | 6.6 |
+| 8 | ProHarvest | 81P19 | VT4PRIB | 265.45 | 19.8 | 55 | 3.2 |
+| 9 | ProHarvest | 82P96 | PCE | 263.8 | 18.7 | 55.1 | 1.5 |
+| 10 | ProHarvest | 79P54 | SSPRO | 263.65 | 16.9 | 57.1 | 1.4 |
+| 11 | ProHarvest | 78P30 | VT2PRIB | 262.21 | 16 | 56.2 | -0.1 |
+| 12 | ProHarvest | 79P87 | SSRIB | 261.28 | 16.7 | 58.8 | -1 |
+| 13 | ProHarvest | 80P75 | PCE | 257.71 | 16.8 | 55.3 | -4.6 |
+| 14 | ProHarvest | 84P41 | PCE | 252.35 | 19.7 | 55.7 | -9.9 |
+| 15 | ProHarvest | 77P25 | VT4PRIB | 250.91 | 14.4 | 56.5 | -11.4 |
+| 16 | ProHarvest | 79P15 | V | 242.78 | 18.4 | 55.4 | -19.5 |
+| 17 | ProHarvest | 78P95 | PCE | 237.73 | 17.6 | 57.5 | -24.6 |
+| 18 | ProHarvest | 76P42 | PCE | 237.51 | 16.9 | 56.8 | -24.8 |
+| 19 | ProHarvest | 81P20 | PCE | 227.35 | 18.1 | 56 | -34.9 |