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-2024-9661.md

@@ -0,0 +1,36 @@
+# Corn yield trial — Panora Acres (Manchester, MD, 2024)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2024
+- **Location:** Manchester, MD · Carroll County
+- **Cooperator:** Panora Acres
+- **Company rep:** Keith Knapp
+- **Planted:** 5/21/2024
+- **Harvested:** 10/19/2024
+- **Previous crop:** Corn
+- **Row width:** 30"
+- **Population:** 33,000 seeds/acre
+- **Tillage:** Strip/Zone
+- **Irrigation:** Non-Irrigated
+- **Fungicide:** No
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2024/11/Corn-ANB-Farms-Manchester-MD-21102.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | ProHarvest | 80P75 | PCE | 252.63 | 21.6 | 53.5 | 23.0 |
+| 2 | ProHarvest | 78P23 | PCE | 246.23 | 20.5 | 55.7 | 16.6 |
+| 3 | ProHarvest | 76P42 | PCE | 244.3 | 20.6 | 54.7 | 14.7 |
+| 4 | ProHarvest | 81P20 | PCE | 243.73 | 21.5 | 52.8 | 14.1 |
+| 5 | ProHarvest | 79P87 | SS RIB | 241.16 | 22.2 | 52.0 | 11.5 |
+| 6 | ProHarvest | 83P17 | PCE | 237.28 | 23.2 | 50.6 | 7.6 |
+| 7 | AgriGold | 64352 | VT2P RIB | 236.54 | 22.8 | 55.4 | 6.9 |
+| 8 | AgriGold | 64352 | VT2P RIB | 236.09 | 22.3 | 56.2 | 6.5 |
+| 9 | ProHarvest | 83P66 | VT2P RIB | 225.11 | 22.8 | 54.1 | -4.5 |
+| 10 | ProHarvest | 85P58 | SS RIB | 222.09 | 21.5 | 56.2 | -7.6 |
+| 11 | ProHarvest | 81P65 | V | 189.21 | 21.5 | 54.9 | -40.4 |
+| 12 | ProHarvest | 73P40 | PCE | 181.3 | 20.4 | 56.7 | -48.3 |