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-78p95.md

@@ -0,0 +1,71 @@
+# 78P95
+
+- **Vendor:** ProHarvest Seeds (independent regional brand)
+- **Brand:** ProHarvest Seeds
+- **Crop:** Corn
+- **Relative maturity:** 108 days
+- **Trait(s):** Conventional, PowerCore
+- **Source:** https://proharvestseeds.com/seed/78p95/
+- **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
+
+- **GDD Pollination:** 1366
+- **GDD Black Layer:** 2540
+- **Pollination for Maturity:** Late
+- **Plant Height:** Medium-Tall
+- **Leaf Type:** Semi-Upright
+- **Ear Height:** Medium
+- **Ear Type:** Semi-Flex
+- **Kernel Rows:** 16-20
+- **Cob Color:** White
+- **Test Weight:** Good
+- **Husk Coverage:** Very Good
+- **Covercrop Companion:** Good
+
+## Agronomic Characteristics
+
+- **Emergence:** Very Good
+- **Seedling Vigor:** Very Good
+- **Dry Down:** Very Good
+- **Stress Tolerance:** Very Good
+- **Delayed Harvest:** Very Good
+- **Response to Fungicide:** Good
+- **Corn After Corn:** Very Good
+- **Silage:** Very Good
+
+## Disease Ratings
+
+- **Grey Leaf Spot:** 8
+- **Northern Corn Leaf Blight:** 8
+- **Southern Leaf Blight:** 8
+- **Common Rust:** 8
+- **Southern Rust:** 7
+- **Eye Spot:** NA
+- **Goss's Wilt:** 8
+- **Stalk Anthracnose:** 8
+- **Diplodia Ear Rot:** 7
+- **Physoderma:** NA
+- **Tar Spot:** 8
+
+## Soil Adaptability
+
+- **Light Soils:** HR
+- **Medium Soils:** HR
+- **Heavy Soils:** HR
+- **Poorly Drained Soils:** R
+
+## Nitrogen Application/Timing
+
+- **Corn/SB 100% Pre:** R
+- **Corn/SB Pre/Side:** HR
+- **Corn/SB Starter/Side:** HR
+- **Corn/Corn 100% Pre:** NR
+- **Corn/Corn Pre/Side:** HR
+- **Corn/Corn Starter/Side:** HR
+- **Corn/Cover 100% Pre:** NR
+- **Corn/Cover Pre/Side:** HR
+- **Corn/Cover Starter/Side:** HR