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-2024-9613.md

@@ -0,0 +1,39 @@
+# Corn yield trial — Wagler Brothers (Montgomery, IN, 2024)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2024
+- **Location:** Montgomery, IN · Daviess County
+- **Cooperator:** Wagler Brothers
+- **Company rep:** Tom Forrest
+- **Planted:** 5/13/2024
+- **Harvested:** 10/10/2024
+- **Previous crop:** Soybeans
+- **Row width:** 34
+- **Population:** 34,000 seeds/acre
+- **Tillage:** Conventional
+- **Irrigation:** Non-Irrigated
+- **Fungicide:** No
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2024/11/Corn-Wagler-Brothers-Montgomery-IN-46321.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | ProHarvest | 85P58 | SSRIB | 243.37 | 15.2 | 60 | 37.3 |
+| 2 | ProHarvest | 8360 | VT2PRIB | 232.4 | 15.5 | 57.6 | 26.3 |
+| 3 | ProHarvest | 84P78 | TRERIB | 230.23 | 14.4 | 58.1 | 24.2 |
+| 4 | Seed Consultants | 1094PCE | - | 227.29 | 13.9 | 56.8 | 21.2 |
+| 5 | Seed Consultants | 1055PCE | - | 217.28 | 12.4 | 56.3 | 11.2 |
+| 6 | ProHarvest | 82P79 | VT2PRIB | 210.55 | 15.3 | 58.7 | 4.5 |
+| 7 | ProHarvest | 83P17 | PCE | 208.14 | 15.1 | 56.6 | 2.1 |
+| 8 | Seed Consultants | 1135 | PCE | 205.6 | 14.4 | 57.3 | -0.5 |
+| 9 | ProHarvest | 83P66 | VT2PRIB | 202.35 | 16 | 55.9 | -3.7 |
+| 10 | ProHarvest | 83P33 | DGVT2PRIB | 197.32 | 14.5 | 57.9 | -8.7 |
+| 11 | Seed Consultants | SC | 1093 AM | 191.54 | 14.1 | 58.2 | -14.5 |
+| 12 | ProHarvest | 81P65 | V | 191.23 | 14.9 | 57.7 | -14.8 |
+| 13 | Seed Consultants | SC | 1183 AM | 187.63 | 14.8 | 56.1 | -18.4 |
+| 14 | Seed Consultants | SC | 1084 AM | 177.61 | 13 | 57.4 | -28.4 |
+| 15 | ProHarvest | 84P30 | AA | 168.27 | 16.6 | 58.7 | -37.8 |