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-2024-9655.md

@@ -0,0 +1,31 @@
+# Soybean yield trial — Larry Reichert (Maria Stein, OH, 2024)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Soybean
+- **Year:** 2024
+- **Location:** Maria Stein, OH · Mercer County
+- **Cooperator:** Larry Reichert
+- **Company rep:** Matthew Reichert
+- **Planted:** 5/21/2024
+- **Harvested:** 9/19/2024
+- **Previous crop:** Corn
+- **Row width:** 30
+- **Population:** 140,000 seeds/acre
+- **Tillage:** Conventional
+- **Irrigation:** Non-Irrigated
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2024/11/Soy-Larry-Reichert-Maria-Stein-OH-45860.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | Apex | AE2950 | - | 73.24 | 9 | None | 2.6 |
+| 2 | Apex | AE2940S | - | 71.55 | 9 | None | 1 |
+| 3 | Apex | AE2930 | - | 71.21 | 9 | None | 0.6 |
+| 4 | Apex | AE2740 | - | 70.93 | 8.5 | None | 0.3 |
+| 5 | ProHarvest | 25E35 | - | 70.63 | 8 | None | 0 |
+| 6 | Apex | AE2750 | - | 69.91 | 8.5 | None | -0.7 |
+| 7 | Apex | AE3131S | - | 68.81 | 9.5 | None | -1.8 |
+| 8 | Apex | AE2930 | - | 68.51 | 9 | None | -2.1 |