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-2024-9537.md

@@ -0,0 +1,38 @@
+# Corn yield trial — Sam & Julie Serven (St. Augustine, IL, 2024)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2024
+- **Location:** St. Augustine, IL · Fulton County
+- **Cooperator:** Sam & Julie Serven
+- **Company rep:** Eric Yoder
+- **Planted:** 5/17/2024
+- **Harvested:** 10/22/2024
+- **Previous crop:** Soybeans
+- **Row width:** 30
+- **Population:** 33,000 seeds/acre
+- **Tillage:** Min-Till
+- **Irrigation:** Non-Irrigated
+- **Fungicide:** Yes
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2024/11/Corn-Sam-Julie-Serven-St-Augustine-IL-61474.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | ProHarvest | 84P78 | TRERIB | 266.9 | 15.7 | 59.4 | 11.4 |
+| 2 | LG Seeds | LG63C32STXRIB | - | 264.7 | 16 | 58.3 | 9.2 |
+| 2 | ProHarvest | 84P78 | TRERIB | 264.7 | 15.8 | 59.4 | 9.2 |
+| 3 | LG Seeds | LG64C43 | VT2RIB | 264.4 | 17.5 | 59 | 8.9 |
+| 3 | ProHarvest | 84P78 | TRERIB | 264.4 | 16.1 | 58 | 8.9 |
+| 4 | ProHarvest | 83P66 | VT2PRIB | 255.9 | 17.6 | 58.1 | 0.4 |
+| 5 | LG Seeds | LG66C44 | VT2PRIB | 255.1 | 16.6 | 59.9 | -0.4 |
+| 6 | LG Seeds | LG62C73VT2P | - | 254.4 | 16.8 | 59.3 | -1.1 |
+| 7 | LG Seeds | LG63C82 | DGVT2 | 254 | 15.1 | 61.3 | -1.5 |
+| 8 | ProHarvest | 81P20 | PCE | 253.1 | 14.2 | 58.3 | -2.4 |
+| 9 | ProHarvest | 83P33 | DGVT2PRIB | 250.3 | 15.6 | 59.2 | -5.2 |
+| 10 | ProHarvest | 85P58 | SSRIB | 248.5 | 16.2 | 63 | -7 |
+| 11 | LG Seeds | LG65C30VT2P | - | 244.3 | 16.3 | 62.6 | -11.2 |
+| 12 | ProHarvest | 84P30 | AA | 236.6 | 17.2 | 59.3 | -18.9 |