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-2024-9492.md

@@ -0,0 +1,40 @@
+# Corn yield trial — Mike VanZee (Sully, IA, 2024)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2024
+- **Location:** Sully, IA · Jasper County
+- **Cooperator:** Mike VanZee
+- **Company rep:** Jake Ekstrand
+- **Planted:** 4/25/2024
+- **Harvested:** 10/7/2024
+- **Previous crop:** Soybeans
+- **Row width:** 30
+- **Population:** 33,500 seeds/acre
+- **Tillage:** No-Till
+- **Irrigation:** Non-Irrigated
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2024/11/Corn-Mike-VanZee-Sully-IA-50251.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | NuTech | 69C7 | PCE | 255.75 | 16.5 | None | 22.3 |
+| 2 | NuTech | 71A7 | V | 252.69 | 17.5 | None | 19.2 |
+| 3 | NuTech | 71A2 | V | 246.85 | 17.2 | None | 13.4 |
+| 4 | NuTech | 74A5 | PCE | 246.28 | 18.6 | None | 12.8 |
+| 5 | NuTech | 70F6 | V | 244.92 | 17 | None | 11.5 |
+| 6 | NuTech | 73A4 | AM | 244.73 | 18.1 | None | 11.3 |
+| 7 | ProHarvest | 83P48 | SSPRO | 244.46 | 19.2 | None | 11 |
+| 8 | NuTech | 70A8 | AM | 244.33 | 17.2 | None | 10.9 |
+| 9 | NuTech | 70B4 | AM | 241.88 | 15.9 | None | 8.4 |
+| 10 | ProHarvest | 83P17 | PCE | 234.2 | 17.5 | None | 0.8 |
+| 11 | ProHarvest | 81P20 | PCE | 224.68 | 17.6 | None | -8.8 |
+| 12 | ProHarvest | 80P75 | PCE | 224.29 | 16.6 | None | -9.2 |
+| 13 | ProHarvest | 84P22 | DV | 219.77 | 19.4 | None | -13.7 |
+| 14 | ProHarvest | 83P66 | VT2PRIB | 216.57 | 24.7 | None | -16.9 |
+| 15 | ProHarvest | 82P79 | VT2PRIB | 213.35 | 18.4 | None | -20.1 |
+| 16 | ProHarvest | 8360 | VT2PRIB | 212.57 | 18.7 | None | -20.9 |
+| 17 | ProHarvest | 79P54 | SSPRO | 201.27 | 17.1 | None | -32.2 |