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/channel-5c42-sorghum.md

@@ -0,0 +1,71 @@
+# 5C42 BRAND
+
+- **Vendor:** Bayer
+- **Brand:** Channel
+- **Crop:** Sorghum
+- **Release year:** 2017
+- **Source:** https://www.cropscience.bayer.us/sorghum/channel/channel-5c42-sorghum
+- **Rating scale (Bayer):** 1-9 (9 = best)
+
+---
+## Strengths & management
+
+- Very good sugarcane aphid tolerance
+- Unique new Early maturity genetics with excellent pre- and post-flower stress tolerance
+- Outstanding yield potential for Early maturity hybrid, even under stressful environments
+- Excellent disease resistance package with very good tolerance to Charcoal Rot, Head Smut and Fusarium Head Blight
+
+## Maturity
+
+| Characteristic | Value |
+|---|---|
+| MATURITY GROUP | Early |
+
+## Agronomic Characteristics
+
+| Characteristic | Value |
+|---|---|
+| MATURITY GROUP | Early |
+| GRAIN COLOR | Cream |
+| YIELD POTENTIAL FOR MATURITY | 1 |
+| NON-IRRIGATED | 2 |
+| IRRIGATED | 3 |
+| APPROXIMATE SEEDS PER POUND (000) | 14.8-16.8 |
+| SEEDLING VIGOR | 3 |
+| DRILL CULTURE | 2 |
+| TOTAL PLANT HEIGHT (IN.) | 42-52 |
+| ROOT LODGING | 2 |
+| PRE-FLOWER STRESS TOLERANCE | 1 |
+| STANDABILITY | 2 |
+| THRESHABILITY | 3 |
+| HEAD EXERTION | 2 |
+| HEAD TYPE | Intermediate |
+| DRYDOWN | 2 |
+| TEST WEIGHT | 3 |
+| POST FREEZE STANDABILITY | 3 |
+| DAYS TO FLOWER | 59 |
+| DAYS TO HARVEST | 105 |
+| GROWTH REGULATORS SENSITIVITY | 4 |
+| HEIGHT UNIFORMITY | 2 |
+
+## Disease Tolerance
+
+| Characteristic | Value |
+|---|---|
+| CHARCOAL ROT | 3 |
+| SUGARCANE APHID TOLERANCE | 3 |
+| FUSARIUM HEAD BLIGHT | 3 |
+
+## Other
+
+| Characteristic | Value |
+|---|---|
+| NEW | No |
+| FEATURED | No |
+| TRAIT | null |
+| VARIETY CODE | A1071963 |
+
+## Regional seed-guide listings
+
+- **Test Guide** — agronomist: Corey Sokol
+- **Demo Guide** — agronomist: Darshit Marwah