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-soybeans-2024-9669.md

@@ -0,0 +1,31 @@
+# Soybean yield trial — Nolan Good (Baring, MO, 2024)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Soybean
+- **Year:** 2024
+- **Location:** Baring, MO · Knox County
+- **Cooperator:** Nolan Good
+- **Company rep:** Jake Ekstrand
+- **Planted:** 4/6/2024
+- **Harvested:** 10/3/2024
+- **Previous crop:** Corn
+- **Row width:** 30
+- **Population:** 160,000 seeds/acre
+- **Tillage:** No-Till
+- **Irrigation:** Non-Irrigated
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2024/11/Soy-Nolan-Good-Baring-MO-63537.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | Apex | AE3550S | - | 70.45 | 10.3 | 54.7 | 10.4 |
+| 2 | Apex | AE3950S | - | 70.04 | 10.2 | 54.6 | 10 |
+| 3 | Partners Brand | PB3925 | - | 69.21 | 10 | 56.9 | 9.2 |
+| 4 | Apex | AE4150S | - | 60.54 | 10.2 | 56.2 | 0.5 |
+| 5 | Partners Brand | PB3622S | - | 59.91 | 10.7 | 55.4 | -0.1 |
+| 6 | Partners Brand | PB4124 | - | 53.09 | 10.7 | 54.8 | -6.9 |
+| 7 | Partners Brand | PB4424 | - | 48.59 | 11.8 | 54.7 | -11.4 |
+| 8 | Partners Brand | PB4624 | - | 48.26 | 12.4 | 54.9 | -11.8 |