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-2024-9625.md

@@ -0,0 +1,52 @@
+# Corn yield trial — Mike Bredemeier (Stella, NE, 2024)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2024
+- **Location:** Stella, NE · Richardson County
+- **Cooperator:** Mike Bredemeier
+- **Company rep:** Trent Geistlinger
+- **Planted:** 4/22/2024
+- **Harvested:** 9/18/2024
+- **Previous crop:** Soybeans
+- **Row width:** 30
+- **Population:** 31,000 seeds/acre
+- **Tillage:** No-Till
+- **Irrigation:** Non-Irrigated
+- **Fungicide:** YES
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2024/11/Corn-Mike-Bredemeier-Stella-NE-68442.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | Pioneer | P1742 | PCE | 257.77 | 21.6 | 54 | 28.2 |
+| 2 | ProHarvest | 77P19 | VT2PRIB | 257.46 | 15.6 | 58.5 | 27.9 |
+| 3 | Pioneer | P1742 | Q | 256.06 | 20.7 | 54.2 | 26.5 |
+| 4 | ProHarvest | 80P75 | PCE | 255.52 | 17.6 | 55.5 | 25.9 |
+| 5 | ProHarvest | 83P33 | DGVT2PRIB | 252.7 | 19.8 | 55.3 | 23.1 |
+| 6 | ProHarvest | 85P58 | SSRIB | 249.58 | 20 | 57.7 | 20 |
+| 7 | ProHarvest | 81P65 | V | 248.47 | 18.3 | 56.6 | 18.9 |
+| 8 | ProHarvest | 76P42 | PCE | 247.56 | 16.2 | 56.7 | 18 |
+| 9 | ProHarvest | 78P23 | PCE | 246.09 | 16.7 | 57.9 | 16.5 |
+| 10 | Hoegemeyer | 8370 | AM | 241.33 | 18.8 | 54.9 | 11.7 |
+| 11 | ProHarvest | 83P48 | SSPRO | 237.8 | 21.1 | 55.2 | 8.2 |
+| 12 | Hoegemeyer | 8453 | AML | 237.1 | 19.5 | 56.2 | 7.5 |
+| 13 | ProHarvest | 77P60 | SSRIB | 236.88 | 15.4 | 57.6 | 7.3 |
+| 14 | ProHarvest | 84P78 | TRERIB | 231.37 | 18.6 | 55.3 | 1.8 |
+| 15 | ProHarvest | 79P49 | VT2PRIB | 229.33 | 16.3 | 58.3 | -0.3 |
+| 16 | Pioneer | P09944 | AM | 227.41 | 17 | 58.1 | -2.2 |
+| 17 | ProHarvest | 8360 | VT2PRIB | 227.11 | 20.1 | 55.6 | -2.5 |
+| 18 | Pioneer | P13050 | AM | 222.79 | 17.6 | 56.1 | -6.8 |
+| 19 | ProHarvest | 79P54 | SSPRO | 222.66 | 16.9 | 57 | -6.9 |
+| 20 | ProHarvest | 79P49 | VT2PRIB | 218.52 | 16.8 | 58.1 | -11.1 |
+| 21 | ProHarvest | 79P87 | SSRIB | 217.86 | 16.3 | 57.8 | -11.7 |
+| 22 | ProHarvest | 83P66VT2PRORIB | - | 217.82 | 20.5 | 55.6 | -11.8 |
+| 23 | ProHarvest | 84P30 | AA | 211.36 | 18.8 | 56.5 | -18.2 |
+| 24 | ProHarvest | 81P20 | PCE | 204.17 | 17.7 | 56.3 | -25.4 |
+| 25 | ProHarvest | 82P68 | SSPRO | 201.44 | 18.8 | 56.9 | -28.2 |
+| 26 | ProHarvest | 83P17 | PCE | 195.73 | 21.1 | 54.1 | -33.9 |
+| 27 | ProHarvest | 82P79 | VT2PRIB | 193.95 | 19.1 | 57.5 | -35.6 |
+| 28 | ProHarvest | 8357 | DGVT2PRIB | 182.74 | 19.4 | 55.3 | -46.9 |