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-2024-9629.md

@@ -0,0 +1,33 @@
+# Corn yield trial — Richard Cool Irrigated (Callaway, NE, 2024)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2024
+- **Location:** Callaway, NE · Custer County
+- **Cooperator:** Richard Cool Irrigated
+- **Company rep:** Derald Watson
+- **Planted:** 5/10/2024
+- **Harvested:** 10/20/2024
+- **Previous crop:** Corn
+- **Row width:** 30"
+- **Population:** 32,000 seeds/acre
+- **Tillage:** Min-Till
+- **Irrigation:** Irrigated
+- **Fungicide:** Yes
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2024/11/Corn-Richard-Cool-Irrigated-Callaway-NE-68825.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | Pioneer | P0662 | Qrome | 229.25 | 18.3 | 56.3 | 5.8 |
+| 2 | Pioneer | P08527 | V | 227.74 | 20.3 | 56.2 | 4.2 |
+| 3 | Pioneer | P05081 | AML | 226.72 | 18.2 | 56.2 | 3.2 |
+| 4 | ProHarvest | 75P85 | SS RIB | 225.97 | 19.4 | 55.8 | 2.5 |
+| 5 | Pioneer | P05466 | V | 225.15 | 18.7 | 55.5 | 1.7 |
+| 6 | Pioneer | P0622 | AML | 222.07 | 18.9 | 55.3 | -1.4 |
+| 7 | Pioneer | P0859 | AM | 221.2 | 21.8 | 55.7 | -2.3 |
+| 8 | ProHarvest | 77P54 | SS RIB | 218.16 | 20.8 | 54.9 | -5.3 |
+| 9 | ProHarvest | 77P60 | SS RIB | 215.14 | 17.8 | 55.8 | -8.3 |