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-2025-9922.md

@@ -0,0 +1,34 @@
+# Corn yield trial — Harm Smith (Forest, IN, 2025)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2025
+- **Location:** Forest, IN · Clinton County
+- **Cooperator:** Harm Smith
+- **Company rep:** David Hopkins
+- **Planted:** 5/12/2025
+- **Harvested:** 10/23/2025
+- **Previous crop:** Soybeans
+- **Row width:** 30
+- **Population:** 32,600 seeds/acre
+- **Tillage:** Conventional
+- **Irrigation:** Non-Irrigated
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2025/10/Corn-Smith-Forest-IN.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | Pioneer | P1170 | AM | 261.44 | 21.4 | None | 10.5 |
+| 2 | ProHarvest | 81P20 | PCE | 256.33 | 19.1 | None | 5.4 |
+| 3 | ProHarvest | 81P45 | TRERIB | 255.94 | 21.3 | None | 5 |
+| 4 | Channel | 213-23 | - | 254.68 | 18.6 | None | 3.8 |
+| 5 | Pioneer | P1383 | AM | 254.64 | 19.3 | None | 3.7 |
+| 6 | ProHarvest | 81P45 | TRERIB | 251.49 | 20.9 | None | 0.6 |
+| 7 | Channel | 213-23 | - | 247.76 | 19 | None | -3.1 |
+| 8 | ProHarvest | 81P45 | TRERIB | 247.11 | 21.1 | None | -3.8 |
+| 9 | Channel | 208-62 | VT2PRIB | 246.52 | 18.6 | None | -4.4 |
+| 10 | ProHarvest | 81P20 | PCE | 245.12 | 20.3 | None | -5.8 |
+| 11 | ProHarvest | 81P20 | PCE | 238.77 | 20.5 | None | -12.1 |