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-2025-9876.md

@@ -0,0 +1,44 @@
+# Corn yield trial — Calvin Good (Azen, MO, 2025)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2025
+- **Location:** Azen, MO · Scotland County
+- **Cooperator:** Calvin Good
+- **Company rep:** Jake Ekstrand
+- **Planted:** 4/17/2025
+- **Harvested:** 10/11/2025
+- **Previous crop:** Soybeans
+- **Row width:** 30
+- **Population:** 32,000 seeds/acre
+- **Tillage:** Conventional
+- **Irrigation:** Non-Irrigated
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2025/10/Corn-Calvin-Good-Azen-MO.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | Becks | 6492 | - | 269.35 | 14.8 | 59.1 | 25.1 |
+| 2 | Channel | 215-42 | TRERIB | 267.65 | 14.8 | 59.5 | 23.4 |
+| 3 | ProHarvest | 86P55 | TRERIB | 265.31 | 16.1 | 57.5 | 21 |
+| 4 | ProHarvest | 86P55 | TRERIB | 258.82 | 15.9 | 55.3 | 14.5 |
+| 5 | Channel | 215-42 | TRERIB | 256.07 | 15.3 | 59.3 | 11.8 |
+| 6 | ProHarvest | 84P78 | TRERIB | 252.4 | 15 | 57.2 | 8.1 |
+| 7 | Channel | 215-70 | TRERIB | 251.79 | 14.4 | 59.1 | 7.5 |
+| 8 | Becks | 6973 | TCV2P | 250.35 | 15 | 58.1 | 6.1 |
+| 9 | Becks | 6700 | VT2P | 247.76 | 14.9 | 60.8 | 3.5 |
+| 10 | Becks | 6473 | TCV2P | 247.16 | 14.4 | 57.7 | 2.9 |
+| 11 | Channel | 215-09 | VT2PRIB | 246.45 | 14.7 | 58.6 | 2.2 |
+| 12 | Pioneer | P1548 | AM | 244.4 | 14.5 | 57.4 | 0.1 |
+| 13 | Becks | 6574 | TCV2P | 242.27 | 14.7 | 58.3 | -2 |
+| 14 | ProHarvest | 85P58 | VT2PRIB | 241.83 | 14.9 | 59.6 | -2.4 |
+| 15 | Pioneer | P14830 | AML | 240.23 | 14.4 | 57.6 | -4 |
+| 16 | AgVenture | 5214 | AM | 236.37 | 14.8 | 56.9 | -7.9 |
+| 17 | Channel | 214-70 | TRERIB | 227.98 | 14.4 | 58.6 | -16.3 |
+| 18 | ProHarvest | 83P66 | VT2PRIB | 227.63 | 14.8 | 57.4 | -16.6 |
+| 19 | Becks | 6374 | V2P | 226.06 | 14.7 | 57.4 | -18.2 |
+| 20 | Channel | 215-72 | TRERIB | 224.77 | 14.5 | 59.9 | -19.5 |
+| 21 | ProHarvest | 83P48 | SSPRO | 205.17 | 15 | 56.9 | -39.1 |