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-2024-9559.md

@@ -0,0 +1,41 @@
+# Corn yield trial — TODD UHMAN (Tremont, IL, 2024)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2024
+- **Location:** Tremont, IL · Tazewell County
+- **Cooperator:** TODD UHMAN
+- **Company rep:** John Walsh
+- **Planted:** 5/22/2024
+- **Harvested:** 10/29/2024
+- **Previous crop:** Soybeans
+- **Row width:** 30"
+- **Population:** 35,000 seeds/acre
+- **Tillage:** Strip/Zone
+- **Irrigation:** Non-Irrigated
+- **Fungicide:** Yes
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2024/11/Corn-Todd-Uhman-Sun-Ag-Tremon-IL-61568.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | Dekalb | 66-06 | TRE RIB | 288.23 | 19.0 | - | 14.4 |
+| 2 | Croplan | 5682 | TRE RIB | 285.96 | 18.3 | - | 12.1 |
+| 3 | Dekalb | 68-35 | VT2P RIB | 282.06 | 18.6 | - | 8.2 |
+| 4 | Brevant | 14H38 | AM | 281.29 | 16.9 | - | 7.5 |
+| 5 | ProHarvest | 83P66 | VT2P RIB | 280.44 | 19.0 | - | 6.6 |
+| 6 | Dekalb | 112-12 | TRE RIB | 278.59 | 17.2 | - | 4.8 |
+| 7 | Dekalb | 110-41 | TRE RIB | 278.29 | 16.2 | - | 4.5 |
+| 8 | Brevant | 08R32 | AM | 276.9 | 14.7 | - | 3.1 |
+| 9 | Dekalb | 64-22 | VT2P RIB | 274.09 | 16.1 | - | 0.3 |
+| 10 | Croplan | 4840 | TRE RIB | 274.06 | 13.8 | - | 0.2 |
+| 11 | Dekalb | 110-10 | SSPRO | 270.18 | 15.7 | - | -3.6 |
+| 12 | Croplan | 5550 | VT2P RIB | 270.16 | 18.0 | - | -3.7 |
+| 13 | Croplan | 4839 | PCE | 265.09 | 15.5 | - | -8.7 |
+| 14 | Dekalb | 66-18 | VT2P RIB | 263.34 | 18.0 | - | -10.5 |
+| 15 | Dekalb | 114-99 | VT4P RIB | 262.84 | 18.6 | - | -11.0 |
+| 16 | Brevant | 13K20 | Qrome | 261.95 | 16.5 | - | -11.9 |
+| 17 | Brevant | 13C49V | PCE | 261.53 | 16.4 | - | -12.3 |