bayer_seeds: add Channel + DEKALB silage/sorghum/canola + Deltapine cotton

User flagged that Channel is expanding into their area — re-walked
the cropscience.bayer.us sitemap and found 8 additional brand×crop
paths beyond the original DEKALB/Asgrow/WestBred triple. Patches
the scraper to walk all of them; total Bayer varieties roughly
doubles from 475 to 931 and the corpus picks up first-ever
coverage in sorghum (36), cotton (30), canola (6), and silage as a
distinct crop (was conflated with corn before).

Net new varieties: 456
  Channel    corn=181  soy=67   silage=54  sorghum=18    (320)
  DEKALB     silage=82 sorghum=18  canola=6              (106)
  Deltapine  cotton=30                                    (30)

scrape/sources/bayer_seeds.py
- Replace `BRANDS` (brand → 1 path) and `CROP_SUFFIX` (brand → 1
  suffix) with a flatter `BRAND_PATHS` list of (brand, url_path,
  crop, is_primary_for_brand) entries. Channel and DEKALB are now
  multi-crop brands; the same scraper walks every brand×crop pair.
- source_key derivation: for a brand's PRIMARY crop, strip the
  trailing `-<crop>` suffix (matches the existing deployed source
  keys for DEKALB corn / Asgrow soy / WestBred wheat). For
  SECONDARY crops, KEEP the suffix so DEKALB-the-same-SKU sold as
  both grain corn and silage gets two distinct source_keys
  (collision-safe and unambiguous for `lookup_variety`).
- New `--crop` CLI filter for incremental backfills.
- Log line shows brand + crop alongside source_key for visibility.

rag/chunk.py
- Channel + Deltapine pages use slightly different characteristics
  group labels (DISEASE not DISEASE RATINGS, AGRONOMIC
  CHARACTERISTICS not GROWTH/HARVEST, plus MATURITY / ADAPTATION /
  HERBICIDES / OTHER). Fold them into the DISEASE / AGRONOMIC /
  MANAGEMENT label sets so the chunker buckets them correctly
  into the standard sections.

Smoke-tested cross-brand × cross-crop queries against the rebuilt
index (5,529 chunks total) — all 6 sample queries surface the
right brand+crop at top-3:
  Channel corn 110 RM       → 210-25TRE BRAND
  Channel soy 2.5 MG IA     → 2622RXF BRAND
  Deltapine cotton XF       → DP 1820 B3XF BRAND
  Sorghum dryland Kansas    → 6B95 BRAND (Channel)
  Silage corn WI dairy      → DKC64-44RIB BRAND BLEND (silage variant)
  Canola Northern Plains    → DK401TL BRAND

Watchtower will pull the new image on the next push; deploy is
unchanged otherwise.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

corpus/bayer_seeds/dekalb-dks43-76-sorghum.md

@@ -0,0 +1,96 @@
+# DKS43-76 BRAND
+
+- **Vendor:** Bayer
+- **Brand:** Dekalb
+- **Crop:** Sorghum
+- **Release year:** 2025
+- **Source:** https://www.cropscience.bayer.us/sorghum/dekalb/dekalb-dks43-76-sorghum
+- **Rating scale (Bayer):** 1-9 (9 = best)
+
+---
+## Positioning
+
+DKS43-76 is a Medium maturity product combining resistance to Downy Mildew with excellent Sugarcane Aphid tolerance
+
+## Strengths & management
+
+- Excellent Sugarcane Aphid tolerance
+- Resistant to Downy Mildew pathotype 3 and 6
+- Excellent Head Smut resistance
+- Great defense against stalk lodging
+
+## Maturity
+
+| Characteristic | Value |
+|---|---|
+| MATURITY GROUP | Medium |
+
+## Agronomic Characteristics
+
+| Characteristic | Value |
+|---|---|
+| HEAD EXERTION | 3 |
+| HEAD TYPE | Semi-Open |
+| HEIGHT UNIFORMITY | 2 |
+| DAYS TO FLOWER | 66 |
+
+## Management
+
+| Characteristic | Value |
+|---|---|
+| MATURITY GROUP | Medium |
+| NEW | Yes |
+| VARIETY CODE | 01107368 |
+
+## Plant Description
+
+| Characteristic | Value |
+|---|---|
+| TOTAL PLANT HEIGHT (IN.) | 44-52 |
+| APPROX. SEEDS PER POUND (000) | 13-15 |
+| GRAIN COLOR | Bronze |
+| DAYS TO FLOWER - PLAINS | 66 |
+| DAYS TO FLOWER - TX AND SE | 66 |
+| DAYS TO HARVEST - PLAINS | 111 |
+| DAYS TO HARVEST - TX AND SE | 108 |
+
+## Diseases
+
+| Characteristic | Value |
+|---|---|
+| CHARCOAL ROT | 1 |
+| DOWNY MILDEW PATHOTYPE 3 & 6 | Resistant |
+| HEAD SMUT RESISTANCE | 1 |
+| SUGARCANE APHID TOLERANCE | 2 |
+| FUSARIUM HEAD BLIGHT | 2 |
+
+## Growth
+
+| Characteristic | Value |
+|---|---|
+| ROOT LODGING | 4 |
+| PRE-FLOWER STRESS TOLERANCE | 2 |
+| POST-FLOWER STRESS TOLERANCE | 1 |
+| YIELD POTENTIAL UNDER STRESS | 2 |
+
+## Harvest
+
+| Characteristic | Value |
+|---|---|
+| TEST WEIGHT | 3 |
+| THRESHABILITY | 2 |
+| YIELD POTENTIAL FOR MATURITY | 1 |
+| PRE-HARVEST SPROUTING & SHATTERING | 5 |
+
+## Regional seed-guide listings
+
+- **Southeast (AL/FL/GA) 2026** — agronomist: Eddie Beasley
+- **Eastern Missouri 2026** — agronomist: Joe Harris
+- **2026 KS and MO** — agronomist: Molly Drimmel
+- **2026 WTX, OK & NM SEED GUIDE** — agronomist: Kagan Randolph
+- **Central Indiana** — agronomist: Corey Sokol
+- **Southeast (AL/FL/GA) 2026#2** — agronomist: Vint Hicks
+- **2025-26 Central Kansas** — agronomist: Jeff Schaef
+- **Mid Atlantic** — agronomist: Bryan Dillehay
+- **2026 E Central, Central & Northern NE** — agronomist: Josh Erwin
+- **2026 South Central/Southwest KS Guide** — agronomist: Holly Thrasher