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-2024-9535.md

@@ -0,0 +1,47 @@
+# Corn yield trial — Premium Ag Partners (Melvin, IL, 2024)
+
+- **Publisher:** ProHarvest Seeds (cross-vendor plot report)
+- **Crop:** Corn
+- **Year:** 2024
+- **Location:** Melvin, IL · Ford County
+- **Cooperator:** Premium Ag Partners
+- **Company rep:** Jake Wilken
+- **Planted:** 4/24/2024
+- **Harvested:** 10/9/2024
+- **Previous crop:** Soybeans
+- **Row width:** 30
+- **Population:** 36,000 seeds/acre
+- **Tillage:** Conventional
+- **Irrigation:** Non-Irrigated
+- **Source PDF:** https://proharvestseeds.com/wp-content/uploads/2024/11/Corn-Premium-Ag-Partners-Melvin-IL-60952.pdf
+
+---
+
+## Results (head-to-head)
+
+| Rank | Brand | Hybrid/Variety | Trait | Yield/Ac | % H2O | Test Wt | +/- Ave |
+|---|---|---|---|---|---|---|---|
+| 1 | AgriGold | A646-30 | VT2PRIB | 309.71 | 20.7 | 54 | 21.9 |
+| 2 | AgriGold | A644-64 | VT2PRIB | 308.53 | 18.7 | 55.5 | 20.7 |
+| 3 | ProHarvest | 84P78 | TRERIB | 297.3 | 19.4 | 57 | 9.5 |
+| 4 | ProHarvest | 80P75 | PCE | 296.58 | 17.6 | 53.8 | 8.7 |
+| 5 | AgriGold | A642-05 | VT2RIB | 296.55 | 20.7 | 54.7 | 8.7 |
+| 6 | AgriGold | A639-03 | VT2PRIB | 296.44 | 18.6 | 55.1 | 8.6 |
+| 7 | Becks | 6557 | CONV | 295.54 | 20.7 | 53.6 | 7.7 |
+| 8 | AgriGold | A643-52 | VT2PRIB | 293.18 | 19.4 | 58.1 | 5.3 |
+| 9 | AgriGold | A636-16 | VT2PRIB | 293.09 | 17.1 | 54.4 | 5.3 |
+| 10 | AgriGold | A643-52 | VT2PRIB | 289.89 | 20.4 | 55.6 | 2.1 |
+| 11 | AgriGold | A645-16 | VT2PRIB | 289.87 | 18.5 | 54 | 2 |
+| 12 | AgriGold | A641-85 | STXRIB | 287.46 | 17.7 | 59.3 | -0.4 |
+| 13 | ProHarvest | 83P66 | VT2PRIB | 286.76 | 18 | 57.4 | -1.1 |
+| 14 | ProHarvest | 81P20 | PCE | 285.35 | 17.4 | 55.7 | -2.5 |
+| 15 | AgriGold | A643-52 | VT2PRIB | 284.32 | 18.7 | 57.9 | -3.5 |
+| 16 | AgriGold | A643-52 | VT2PRIB | 284.24 | 19.7 | 58 | -3.6 |
+| 17 | ProHarvest | 77P60 | SSRIB | 283.31 | 15.6 | 57.2 | -4.5 |
+| 18 | ProHarvest | 79P87 | SSRIB | 282.36 | 16.2 | 58.1 | -5.5 |
+| 19 | ProHarvest | 85P58 | SSRIB | 282.14 | 17 | 62.8 | -5.7 |
+| 20 | Becks | 6219PQ | - | 280.51 | 18.4 | 56.4 | -7.3 |
+| 21 | ProHarvest | 83P17 | PCE | 278.78 | 19.4 | 55.4 | -9.1 |
+| 22 | ProHarvest | 8360 | CONV | 277.37 | 18.3 | 56.6 | -10.5 |
+| 23 | AgriGold | A637-72 | - | 264.95 | 15.5 | 59.6 | -22.9 |
+| 24 | AgriGold | A643-52 | - | 263.84 | 20.9 | 54.2 | -24 |