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/proharvest-31e65s.md

@@ -0,0 +1,62 @@
+# 31E65S
+
+- **Vendor:** ProHarvest Seeds (independent regional brand)
+- **Brand:** ProHarvest Seeds
+- **Crop:** Soybeans
+- **Maturity group:** 3.1
+- **Trait(s):** Enlist E3
+- **Source:** https://proharvestseeds.com/seed/31e65s/
+- **Rating scale:** disease 1-9, 9=best/most-tolerant, NA=not rated; agronomic/general qualitative (Excellent/Very Good/Good/Average); soil HR=highly recommended/R=recommended
+- **Service area:** Independent dealer network — Eastern/Central Corn Belt (IL/IN/OH/MO/IA/KS/NE)
+
+---
+
+## General Characteristics
+
+- **Plant Height:** Medium
+- **Canopy/Plant Type:** Medium-Bush
+- **Branching Habit:** Branchy
+- **Flower Color:** White
+- **Hilum Color:** Buff
+- **Pod Color:** Tan
+- **Pubescence:** Gray
+- **Protein:** NA
+- **Oil:** NA
+
+## Agronomic Characteristics
+
+- **Yield for Maturity:** Very Good
+- **Emergence:** Excellent
+- **Shatter Resistance:** Very Good
+- **SCN Resistance Source:** Peking
+- **Phytophthora Resistance Source:** 1c
+
+## Disease Ratings
+
+- **Brown Stem Rot:** 9
+- **Root Knot:** NA
+- **Frogeye Leaf Spot:** NA
+- **Stem Canker:** NA
+- **Iron Chlorosis:** 8
+- **Phytophthora Field Resistance:** 8
+- **SDS Tolerance:** 7
+- **White Mold:** 7
+
+## Soil Adaptability
+
+- **Light Soils:** HR
+- **Medium Soils:** HR
+- **Heavy Soils:** HR
+- **Poorly Drained Soils:** HR
+
+## Recommended Seeding Rates
+
+- **30" Low:** R
+- **30" Medium:** HR
+- **30" High:** R
+- **15" Low:** NR
+- **15" Medium:** HR
+- **15" High:** R
+- **7.5" Low:** NR
+- **7.5" Medium:** NR
+- **7.5" High:** R