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-2025-9963.json

@@ -0,0 +1,115 @@
+{
+  "source": "proharvest_plots",
+  "source_key": "phpr-soybeans-2025-9963",
+  "data_type": "trial",
+  "vendor": "ProHarvest Seeds",
+  "brand": "ProHarvest Seeds",
+  "crop": "soybeans",
+  "state": "NE",
+  "state_abbrev": "ne",
+  "city": "Gladstone",
+  "county": "Jefferson",
+  "year": 2025,
+  "plot_id": 9963,
+  "cooperator": "Vonderfecht Brothers",
+  "latitude": 40.16014932483678,
+  "longitude": -97.30667843610219,
+  "company_representative": "Trent Geistlinger",
+  "planted_date": "5/15/2025",
+  "harvested_date": "10/23/2025",
+  "previous_crop": "Corn",
+  "row_width": "15",
+  "population_seeds_per_acre": 150000,
+  "fungicide": null,
+  "herbicide": null,
+  "insecticide": null,
+  "tillage": "No-Till",
+  "irrigation": "Non-Irrigated",
+  "results": [
+    {
+      "brand": "ProHarvest",
+      "rank": 1,
+      "product": "38F67",
+      "traits": null,
+      "metrics": {
+        "Seed Trtmt.": "proTect Ultra",
+        "% H2O": 9,
+        "Test Wt.": 57.1,
+        "Yield": 75.24,
+        "+/- Ave": 5.1
+      }
+    },
+    {
+      "brand": "ProHarvest",
+      "rank": 2,
+      "product": "36F58",
+      "traits": null,
+      "metrics": {
+        "Seed Trtmt.": "proTect Ultra",
+        "% H2O": 9.1,
+        "Test Wt.": 56.4,
+        "Yield": 73.96,
+        "+/- Ave": 3.8
+      }
+    },
+    {
+      "brand": "ProHarvest",
+      "rank": 3,
+      "product": "38F67",
+      "traits": null,
+      "metrics": {
+        "Seed Trtmt.": "proTect Ultra",
+        "% H2O": 9.2,
+        "Test Wt.": 56.9,
+        "Yield": 73.08,
+        "+/- Ave": 2.9
+      }
+    },
+    {
+      "brand": "ProHarvest",
+      "rank": 4,
+      "product": "29F62",
+      "traits": null,
+      "metrics": {
+        "Seed Trtmt.": "proTect Ultra",
+        "% H2O": 9.3,
+        "Test Wt.": 56.6,
+        "Yield": 68.21,
+        "+/- Ave": -1.9
+      }
+    },
+    {
+      "brand": "ProHarvest",
+      "rank": 5,
+      "product": "27F66",
+      "traits": null,
+      "metrics": {
+        "Seed Trtmt.": "protTect D-I",
+        "% H2O": 9.1,
+        "Test Wt.": 56.9,
+        "Yield": 67.16,
+        "+/- Ave": -3
+      }
+    },
+    {
+      "brand": "ProHarvest",
+      "rank": 6,
+      "product": "32F54",
+      "traits": null,
+      "metrics": {
+        "Seed Trtmt.": "protTect D-I",
+        "% H2O": 9.5,
+        "Test Wt.": 56.9,
+        "Yield": 63.28,
+        "+/- Ave": -6.9
+      }
+    }
+  ],
+  "n_results": 6,
+  "raw_text": false,
+  "source_urls": [
+    "https://proharvestseeds.com/wp-content/uploads/2025/10/Soy-Vonderfecht-Bros-Gladstone-NE.pdf"
+  ],
+  "fetched_at": "2026-06-05T00:58:43.304402+00:00",
+  "scraper_version": "0.1.0"
+}