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-2024-9663.md

@@ -0,0 +1,40 @@
+# Corn yield trial — Nolan Good (Baring, MO, 2024)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2024
+- **Location:** Baring, MO · Knox County
+- **Cooperator:** Nolan Good
+- **Company rep:** Jake Ekstrand
+- **Planted:** 5/30/2024
+- **Harvested:** 10/26/2024
+- **Previous crop:** Soybeans
+- **Row width:** 30
+- **Population:** 32,000 seeds/acre
+- **Tillage:** Conventional
+- **Irrigation:** Non-Irrigated
+- **Fungicide:** Aquila XL
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2024/11/Corn-Nolan-Good-Baring-MO-63537.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | ProHarvest | 85P13 | CONV | 222.84 | 18.9 | 52.1 | 27.5 |
+| 2 | Partners Brand | 8014 | CONV | 217.71 | 17.3 | 50.7 | 22.4 |
+| 3 | Partners Brand | 8436 | CONV | 216.25 | 21.3 | 49.5 | 20.9 |
+| 4 | Partners Brand | 8366 | CONV | 211.39 | 19.7 | 52.3 | 16.1 |
+| 5 | ProHarvest | 8360 | CONV | 210.32 | 19 | 54.4 | 15 |
+| 6 | ProHarvest | 80P75 | CONV | 205.24 | 17.2 | 50.2 | 9.9 |
+| 7 | ProHarvest | 81P20 | CONV | 203.93 | 19.6 | 50.1 | 8.6 |
+| 8 | ProHarvest | 8360 | CONV | 190.38 | 20.1 | 51.4 | -4.9 |
+| 9 | ProHarvest | 81P65 | CONV | 189.49 | 18.5 | 51.1 | -5.8 |
+| 10 | ProHarvest | 81P20 | CONV | 187.95 | 16.4 | 53.4 | -7.4 |
+| 11 | ProHarvest | 85P13 | CONV | 183.16 | 19.9 | 47.1 | -12.2 |
+| 12 | ProHarvest | 83W13 | WAXY | 182.62 | 17.5 | 59 | -12.7 |
+| 13 | ProHarvest | 80P75 | CONV | 181.33 | 20.7 | 45.9 | -14 |
+| 14 | ProHarvest | 78P23 | CONV | 178.92 | 17.6 | 49.1 | -16.4 |
+| 15 | Partners Brand | 8264 | WAXY | 173.4 | 18.7 | 56.3 | -21.9 |
+| 16 | Partners Brand | 7783 | CONV | 170.07 | 18.8 | 51.3 | -25.2 |