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-2024-9565.md

@@ -0,0 +1,38 @@
+# Corn yield trial — Tyler Deal (Danvers, IL, 2024)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2024
+- **Location:** Danvers, IL · McLean County
+- **Cooperator:** Tyler Deal
+- **Company rep:** Rick Urish
+- **Planted:** 5/25/2024
+- **Harvested:** 10/24/2024
+- **Previous crop:** Soybeans
+- **Row width:** 30"
+- **Population:** 36,000 seeds/acre
+- **Irrigation:** Non-Irrigated
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2024/11/Corn-Tyler-Deal-Danvers-IL-61732.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | ProHarvest | 84P78TRERIB | TRE RIB | 286.7 | 17.8 | 58.4 | 21.6 |
+| 2 | AgriGold | A642-05VT2RIBD1 | DGVT2P RIB | 285.1 | 17.1 | 59.2 | 20.0 |
+| 3 | AgriGold | A644-64VT2RIB | VT2P RIB | 284.7 | 18.1 | 58.4 | 19.6 |
+| 4 | AgriGold | A643-52VT2RIB | VT2P RIB | 282.2 | 16.8 | 60.8 | 17.1 |
+| 5 | AgriGold | A642-32VT2PRO | VT2P RIB | 281.2 | 17.2 | 61.4 | 16.1 |
+| 6 | AgriGold | A645-30VT2PRO | VT2P RIB | 277.3 | 17.8 | 62.4 | 12.2 |
+| 7 | AgriGold | A647-42TRCRIB | TRE RIB | 277.0 | 20.0 | 56.6 | 11.9 |
+| 8 | AgriGold | A645-16VT2RIB | VT2P RIB | 272.2 | 18.1 | 58.0 | 7.1 |
+| 9 | ProHarvest | 83P66VT2RIB | VT2P RIB | 266.5 | 17.7 | 59.1 | 1.4 |
+| 10 | AgriGold | A642-18SSP | SSPRO | 264.3 | 17.4 | 59.2 | -0.8 |
+| 11 | AgriGold | A645-16 | CONV | 263.3 | 18.1 | 58.0 | -1.8 |
+| 12 | AgriGold | J6015PWE | PCE | 254.0 | 15.4 | 60.4 | -11.1 |
+| 13 | AgriGold | A646-30 | CONV | 251.8 | 16.9 | 59.7 | -13.3 |
+| 14 | AgriGold | A646-30VT2RIB | VT2P RIB | 242.2 | 17.1 | 58.8 | -22.9 |
+| 15 | AgriGold | A645-71STXRIB | SS RIB | 229.2 | 17.4 | 60.7 | -35.9 |
+| 16 | AgriGold | A648-11 | CONV | 223.8 | 20.2 | 56.6 | -41.3 |