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-2025-9934.md

@@ -0,0 +1,41 @@
+# Corn yield trial — Matt Znaniecki (Ottawa, IL, 2025)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2025
+- **Location:** Ottawa, IL · La Salle County
+- **Cooperator:** Matt Znaniecki
+- **Company rep:** Jeff Horner
+- **Planted:** 4/29/2025
+- **Harvested:** 10/1/2025
+- **Previous crop:** Soybeans
+- **Row width:** 30"
+- **Population:** 35,000 seeds/acre
+- **Tillage:** Conventional
+- **Fungicide:** Miravis Neo
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2025/10/Corn-Znaniecki-Ottawa-IL.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | Becks | 6258V4P | VT4P RIB | 242.49 | 14.4 | 60.9 | 16.6 |
+| 2 | Becks | 6469V2P | VT2P RIB | 241.5 | 15.5 | 59.3 | 15.6 |
+| 3 | Becks | 6344SXP | SSPRO | 238.27 | 13.9 | 61.7 | 12.4 |
+| 4 | Becks | 6485SX | SS RIB | 237.73 | 13.9 | 59.5 | 11.9 |
+| 5 | Becks | 6492TCV2P | VT2P RIB | 234.46 | 14.5 | 59.3 | 8.6 |
+| 6 | Becks | 6473TCV2P | VT2P RIB | 231.49 | 13.4 | 60.0 | 5.6 |
+| 7 | ProHarvest | 82P96 | PCE | 229.24 | 14.4 | 58.0 | 3.4 |
+| 8 | Becks | 6064AM™* | AM | 226.74 | 14.0 | 56.5 | 0.9 |
+| 9 | Becks | 6233PCE | PCE | 226.26 | 14.1 | 58.6 | 0.4 |
+| 10 | ProHarvest | 78P95 | PCE | 224.14 | 14.5 | 60.1 | -1.7 |
+| 11 | Becks | 6041Q™* | Qrome | 223.88 | 12.8 | 58.4 | -2.0 |
+| 12 | Becks | 5608AM™* | AM | 219.75 | 12.3 | 59.0 | -6.1 |
+| 13 | Becks | 5686BZ | AA | 218.77 | 13.3 | 56.7 | -7.1 |
+| 14 | Becks | 5864PCE | PCE | 216.64 | 13.5 | 58.1 | -9.2 |
+| 15 | Becks | 6005V™* | VCE | 216.31 | 12.8 | 58.4 | -9.6 |
+| 16 | Becks | 5802D2 | DV | 213.05 | 13.1 | 60.6 | -12.8 |
+| 17 | Becks | 6133V™* | VCE | 212.84 | 14.5 | 57.3 | -13.0 |
+| 18 | Becks | 5324PCE | PCE | 212.16 | 12.7 | 56.5 | -13.7 |