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-2024-9511.md

@@ -0,0 +1,41 @@
+# Corn yield trial — Jeff Brockman (Ransom, IL, 2024)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2024
+- **Location:** Ransom, IL · LaSalle County
+- **Cooperator:** Jeff Brockman
+- **Company rep:** John Walsh
+- **Planted:** 5/20/2024
+- **Harvested:** 10/18/2024
+- **Previous crop:** Soybeans
+- **Row width:** 30"
+- **Population:** 34,000 seeds/acre
+- **Tillage:** Strip/Zone
+- **Fungicide:** Yes
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2024/11/Corn-Brockman-Random-IL-60470.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | AgriGold | 645-71 | SS RIB 20.2 N/A | 294.12 | - | - | 20.1 |
+| 2 | Dekalb | 64-64 | SS RIB 18.6 N/A | 289.74 | - | - | 15.8 |
+| 3 | Wyffels | 7759 | SSPRO 18.9 N/A | 284.95 | - | - | 11.0 |
+| 4 | Dekalb | 110-10 | SS RIB 17.7 N/A | 283.49 | - | - | 9.5 |
+| 5 | Dekalb | 112-29 | SSPRO 18.4 N/A | 282.02 | - | - | 8.0 |
+| 6 | Dekalb | 64-21 | SS RIB 20.4 N/A | 278.76 | - | - | 4.8 |
+| 7 | ProHarvest | 79P54 | SSPRO 18.0 N/A | 278.69 | - | - | 4.7 |
+| 8 | Wyffels | 6479 | SSPRO 17.6 N/A | 276.27 | - | - | 2.3 |
+| 9 | ProHarvest | 83P48 | SSPRO 20.2 N/A | 275.8 | - | - | 1.8 |
+| 10 | Wyffels | 7878 | SS RIB 19.1 N/A | 274.03 | - | - | 0.0 |
+| 11 | ProHarvest | 81P65 | D 18.6 N/A | 273.85 | - | - | -0.1 |
+| 12 | Dekalb | 59-81 | SS RIB 17.0 N/A | 272.56 | - | - | -1.4 |
+| 13 | ProHarvest | 85P58 | SS RIB 19.9 N/A | 270.4 | - | - | -3.6 |
+| 14 | ProHarvest | 77P60 | SS RIB 15.6 N/A | 269.41 | - | - | -4.6 |
+| 15 | Dekalb | 108-64 | SSPRO 16.3 N/A | 263.33 | - | - | -10.6 |
+| 16 | ProHarvest | 82P68 | SSPRO 18.5 N/A | 262.96 | - | - | -11.0 |
+| 17 | Wyffels | 5778 | SS RIB 16.6 N/A | 259.51 | - | - | -14.5 |
+| 18 | ProHarvest | 75P85 | SS RIB 15.8 N/A | 241.7 | - | - | -32.3 |