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-2025-9846.json

@@ -0,0 +1,36 @@
+{
+  "source": "proharvest_plots",
+  "source_key": "phpr-soybeans-2025-9846",
+  "data_type": "trial",
+  "vendor": "ProHarvest Seeds",
+  "brand": "ProHarvest Seeds",
+  "crop": "soybeans",
+  "state": "IL",
+  "state_abbrev": "il",
+  "city": null,
+  "county": "Dekalb",
+  "year": 2025,
+  "plot_id": 9846,
+  "cooperator": "Dekalb County Corn and Soybean Growers",
+  "latitude": 41.929355127532716,
+  "longitude": -88.76308528781375,
+  "company_representative": null,
+  "planted_date": null,
+  "harvested_date": null,
+  "previous_crop": null,
+  "row_width": null,
+  "population_seeds_per_acre": null,
+  "fungicide": null,
+  "herbicide": null,
+  "insecticide": null,
+  "tillage": null,
+  "irrigation": null,
+  "results": [],
+  "n_results": 0,
+  "raw_text": true,
+  "source_urls": [
+    "https://proharvestseeds.com/wp-content/uploads/2025/10/Soy-Dekalb-Co-Corn-and-Soybean-Growers-min.pdf"
+  ],
+  "fetched_at": "2026-06-05T01:00:04.351822+00:00",
+  "scraper_version": "0.1.0"
+}