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-2025-9884.md

@@ -0,0 +1,44 @@
+# Corn yield trial — Jordan Dutter (Flora, IN, 2025)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2025
+- **Location:** Flora, IN · Carroll County
+- **Cooperator:** Jordan Dutter
+- **Company rep:** David Hopkins
+- **Planted:** 4/25/2025
+- **Harvested:** 10/17/2025
+- **Row width:** 30
+- **Tillage:** Conventional
+- **Irrigation:** Non-Irrigated
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2025/10/Corn-Dutter-Flora-IN.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | DEKALB | DKC64-22RIB | - | 267.03 | 16.7 | 63.5 | 16.5 |
+| 2 | ProHarvest | 83P66 | VT2PRIB | 266.41 | 17.4 | 59.2 | 15.9 |
+| 3 | ProHarvest | 83P66 | VT2PRIB | 264.5 | 18.5 | 59.6 | 14 |
+| 4 | DEKALB | DKC63-91RIB | - | 262.99 | 17.1 | 60.8 | 12.5 |
+| 5 | Croplan | CP5497 | VT2P | 262.63 | 16.8 | 62.1 | 12.1 |
+| 6 | ProHarvest | 83P66 | VT2PRIB | 261.68 | 17.6 | 60.6 | 11.2 |
+| 7 | Pioneer | P13777 | PCE | 258.4 | 17.6 | 61.1 | 7.9 |
+| 8 | Brevant | B10A20 | AM | 257.99 | 17.2 | 60.1 | 7.5 |
+| 9 | Pioneer | P1742 | PCE | 253.77 | 16.6 | 59.9 | 3.2 |
+| 10 | Pioneer | P0953 | AM | 252.07 | 15.4 | 59.8 | 1.5 |
+| 11 | Pioneer | P14364 | PCUE | 251.35 | 17.6 | 58.6 | 0.8 |
+| 12 | Dyna-Gro | 48SS-50 | - | 249.89 | 16.5 | 59.4 | -0.6 |
+| 13 | Dyna-Gro | 55-VC80 | - | 249.06 | 18 | 59.5 | -1.5 |
+| 14 | Pioneer | P10477 | V | 248.66 | 16.3 | 59.3 | -1.9 |
+| 15 | DEKALB | DKC111-35RIB | - | 248.47 | 15.7 | 63.2 | -2.1 |
+| 16 | Dyna-Gro | 49-VC70 | - | 245.75 | 16.9 | 60.5 | -4.8 |
+| 17 | Brevant | B13A10 | AM | 244.06 | 16 | 62.6 | -6.5 |
+| 18 | Dyna-Gro | 53-VC54 | - | 243.64 | 17.9 | 60.3 | -6.9 |
+| 19 | Dairyland | DS-4969 | PCE | 243.19 | 16.3 | 58.8 | -7.3 |
+| 20 | Pioneer | P10811 | AM | 239.12 | 15.5 | 58.5 | -11.4 |
+| 21 | Dyna-Gro | 51-VC95 | - | 238.43 | 17.1 | None | -12.1 |
+| 22 | Pioneer | P1383 | AM | 229.55 | 15.6 | 61 | -21 |
+| 23 | Dairyland | DS-5128 | PCE | 223.48 | 16.1 | 60 | -27 |