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-soybeans-2024-9653.md

@@ -0,0 +1,37 @@
+# Soybean yield trial — Grow It to Show It (Delphos, OH, 2024)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Soybean
+- **Year:** 2024
+- **Location:** Delphos, OH · Van Wert County
+- **Cooperator:** Grow It to Show It
+- **Company rep:** Matthew Reichert
+- **Planted:** 5/19/2024
+- **Harvested:** 10/6/2024
+- **Previous crop:** Corn
+- **Row width:** 15"
+- **Population:** 165,000 seeds/acre
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2024/11/Soy-Grown-It-2-Show-It-Delphos-OH-45833.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | Apex | AE3150 | E3 | 75.0 | 11.9 | 58.0 | 6.4 |
+| 2 | LG | Seeds | LGS3216E3 E3 | 73.0 | 12.0 | 58.5 | 4.4 |
+| 3 | LG | Seeds | LGS3445E3 E3 | 72.4 | 12.1 | 59.0 | 3.8 |
+| 4 | Apex | AE2950 | E3 | 70.6 | 12.0 | 59.5 | 2.0 |
+| 5 | LG | Seeds | LGS2881E3 E3 | 70.1 | 12.0 | 58.25 | 1.5 |
+| 6 | LG | Seeds | LGS3000E3 E3 | 69.6 | 11.7 | 58.75 | 1.0 |
+| 7 | Apex | AE2440 | E3 | 68.6 | 11.8 | 57.0 | 0.0 |
+| 7 | Apex | AE3330S | E3 | 68.6 | 11.9 | 58.0 | 0.0 |
+| 9 | Apex | AE2750 | E3 | 68.1 | 11.8 | 58.5 | -0.5 |
+| 9 | LG | Seeds | LGS3688E3 E3 | 68.1 | 12.2 | 58.5 | -0.5 |
+| 11 | Apex | AE3131S | E3 | 67.6 | 11.6 | 58.5 | -1.0 |
+| 12 | Apex | AE2740 | E3 | 67.2 | 12.0 | 59.25 | -1.4 |
+| 12 | ProHarvest | 31E37 | E3 | 67.2 | 11.7 | 57.5 | -1.4 |
+| 14 | ProHarvest | 25E35 | E3 | 65.2 | 11.7 | 57.5 | -3.4 |
+| 15 | LG | Seeds | LGS2505E3 E3 | 64.7 | 11.7 | 57.5 | -3.9 |
+| 16 | Apex | AE2600 | E3 | 61.8 | 12.1 | 58.25 | -6.8 |