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-2024-9503.md

@@ -0,0 +1,44 @@
+# Corn yield trial — Andrew Wright (Ransom, IL, 2024)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2024
+- **Location:** Ransom, IL · LaSalle County
+- **Cooperator:** Andrew Wright
+- **Company rep:** John Walsh
+- **Planted:** 4/22/2024
+- **Harvested:** 9/19/2024
+- **Previous crop:** Soybeans
+- **Row width:** 30"
+- **Population:** 34,000 seeds/acre
+- **Tillage:** Conventional
+- **Irrigation:** Non-Irrigated
+- **Fungicide:** Yes
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2024/11/Corn-Andy-Kurt-Wright-Random-IL-60470.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | Pioneer | P10477V | VCE | 261.31 | 14.8 | - | 13.5 |
+| 2 | ProHarvest | 79P54 | STAXPRO SSPRO | 259.96 | 15.6 | - | 12.1 |
+| 3 | Pioneer | P1742Q | Qrome | 259.69 | 18.5 | - | 11.9 |
+| 4 | Dekalb | DKC108-64RIB | SSPRO | 259.34 | 15.8 | - | 11.5 |
+| 5 | Pioneer | P09312V | VCE | 257.69 | 15.5 | - | 9.9 |
+| 6 | Pioneer | P08527V | VCE | 253.62 | 15.7 | - | 5.8 |
+| 7 | Dekalb | DKC114-99RIB | VT4P RIB | 253.5 | 14.3 | - | 5.7 |
+| 8 | Pioneer | P14830Q | Qrome | 251.94 | 17.1 | - | 4.1 |
+| 9 | Dekalb | DKC56-26RIB | TRE RIB | 251.73 | 14.7 | - | 3.9 |
+| 10 | Pioneer | P0529Q | Qrome | 249.29 | 15.1 | - | 1.5 |
+| 11 | Pioneer | P10625V | VCE | 248.52 | 17.3 | - | 0.7 |
+| 12 | Pioneer | P04511V | VCE | 247.65 | 14.9 | - | -0.2 |
+| 13 | Pioneer | P12065Q | Qrome | 246.41 | 16.5 | - | -1.4 |
+| 14 | Dekalb | DKC66-06RIB | TRE RIB | 245.44 | 19.1 | - | -2.4 |
+| 15 | ProHarvest | 83P48 | STAXPRO SSPRO | 241.92 | 18.6 | - | -5.9 |
+| 16 | ProHarvest | 81P65 | D D | 240.96 | 17.0 | - | -6.9 |
+| 17 | Dekalb | DKC64-22RIB | VT2P RIB | 240.63 | 14.6 | - | -7.2 |
+| 18 | Pioneer | P13777V | VCE | 236.69 | 20.8 | - | -11.1 |
+| 19 | Dekalb | DKC105-33RIB | SSPRO | 227.49 | 16.5 | - | -20.3 |
+| 20 | Dekalb | DKC62-69RIB | SS RIB | 222.8 | 17.0 | - | -25.0 |