Two new trial sources: LG Seeds + AgriGold plot reports (+2,307 cross-vendor yield trials)

Adds the **first non-Syngenta trial coverage** to the corpus:

| Source | Docs | Publisher | URL pattern |
|---|---|---|---|
| lg_plot_reports | 1,304 | LG Seeds (AgReliant) | lgseeds.com/performance/{crop} JSON XHR |
| agrigold_plot_reports | 1,003 | AgriGold (AgReliant) | agrigold.com/{crop}/performance/{crop}-yield-results |

Total trial coverage now: gh_plot_reports (4,299) + agripro_trials (14) +
lg_plot_reports (1,304) + agrigold_plot_reports (1,003) = 6,620 trial docs.

**Both scrapers follow the gh_plot_reports template** — same RateLimitedSession
primitive, same TrialResult/PlotReport dataclass shape, same data_type="trial"
sidecar convention. The trial chunker (`rag/chunk.py:_render_trial_chunk`) is
extended to recognize both new sources; they share `_render_gh_plot_chunk`
since their sidecars are structurally identical (just different brand label).

**LG specifics:**
- POST `/performance/{crop}/GetPlots/` returns sparse listing (id, year, lat/lng)
- GET `/performance/{crop}/GetPlotData/?PlotId=X&IsSilage=Y` returns full detail
  with state, cooperator, planting/harvest dates, and **top-5 hybrids** (LG +
  competitors). Top-5 is what LG publishes publicly; not the full ranking.
- 4 crops: corn (963), soybeans (287), sorghum (10), silage (50) — first
  alfalfa absent because LG doesn't run alfalfa plots; that's variety-only data.
- 301 gotcha: www.lgseeds.com redirects to lgseeds.com which drops POST body,
  so the scraper hits the apex host directly.

**AgriGold specifics:**
- Listing: GET `/{crop}/performance/{crop}-yield-results?harvestYear={year}`
  (server-rendered HTML, ~1MB; 408 corn plots in 2025 alone)
- Detail: GET `/{crop_url}/performance/{slug}/{plot_id}` returns the **full
  ranking** (not just top-5) plus rich plot management metadata: tillage,
  previous crop, fungicide, herbicide, insecticide, irrigation, soil type,
  row width, population. Most metadata-rich of the three trial sources.
- Soybean URL slug is singular: `/soybeans/performance/soybean-yield-results/`
- Columns: Rank | Brand | Product | Trait | Ck | H20 (moisture) | Test Wt. |
  Yield | Adj Yield (check-adjusted)
- 2 crops: corn (849) + soybeans (157)

**Indexer needs no changes** — `rag/index.py` auto-discovers any directory
under corpus/ and routes by data_type. Both new sources flow into the
existing trial collection and surface via `search_trials`.

Years scraped: 2024+2025 (matching gh_plot_reports baseline). 2023 is
available via `--include-2023` on either scraper for future backfill.

corpus/agrigold_plot_reports/agpr-soybeans-2025-147387.md

@@ -0,0 +1,60 @@
+# Soybean yield trial — Franklin Grove, IL, 2025
+
+- **Source:** AgriGold plot report (cross-vendor head-to-head)
+- **Vendor:** AgReliant Genetics / AgriGold
+- **Crop:** Soybean
+- **State:** IL
+- **County:** Lee
+- **City:** Franklin Grove
+- **Year:** 2025
+- **Plot ID:** 147387
+- **Cooperator:** Ag View FS, Inc.
+- **Plot average:** 82.58 BU/Ac
+- **Planted:** 2025-05-10
+- **Harvested:** 2025-10-05
+- **Population:** 150,000 seeds/acre
+- **Row width:** 15.0"
+- **# Rows:** 4
+- **Soil type:** Silt Loam
+- **Tillage:** Minimum
+- **Previous crop:** Corn
+- **Irrigation:** None
+- **URL:** https://www.agrigold.com/soybeans/performance/soybean-yield-results/147387
+
+---
+## Results (by rank)
+
+| Rank | Brand | Product | Trait | Ck | H20 | Test Wt. | Yield | Adj Yield |
+|---|---|---|---|---|---|---|---|---|
+| 1 | FS Seeds | HS29F50 | XTENDFlex | - | 9.5 | - | 90.5 | 90.5 |
+| 2 | Brevant Seeds | B315EE | Enlist E3 | - | 9.3 | - | 89.6 | 89.6 |
+| 3 | AgriGold | G2574XF | XTENDFlex | - | 9.6 | - | 87.3 | 87.3 |
+| 4 | Brevant Seeds | B324EE | Enlist E3 | - | 9.5 | - | 86.5 | 86.5 |
+| 5 | FS Seeds | HS26E50 | Enlist E3 | - | 9.3 | - | 85.9 | 85.9 |
+| 6 | FS Seeds | HS28E50 | Enlist E3 | - | 9.2 | - | 85.5 | 85.5 |
+| 7 | Brevant Seeds | B275EE | Enlist E3 | - | 9.6 | - | 85.4 | 85.4 |
+| 8 | NK Brand | NK26-Z1XF | XTENDFlex | - | 9.6 | - | 85.2 | 85.2 |
+| 9 | NK Brand | NK26-M6E3 | Enlist E3 | - | 9.8 | - | 85.0 | 85.0 |
+| 10 | NK Brand | NK24-U5XF | XTENDFlex | - | 9.7 | - | 84.6 | 84.6 |
+| 11 | NK Brand | NK29-Q3XF | XTENDFlex | - | 9.4 | - | 84.5 | 84.5 |
+| 12 | FS Seeds | HS25E30 | Enlist E3 | - | 9.7 | - | 84.2 | 84.2 |
+| 13 | AgriGold | G3051E3 | Enlist E3 | - | 9.6 | - | 83.3 | 83.3 |
+| 14 | NK Brand | NK28-G7E3S | Enlist E3 | - | 9.5 | - | 83.0 | 83.0 |
+| 14 | Asgrow | AG22XF6 | XTENDFlex | - | 9.7 | - | 83.0 | 83.0 |
+| 16 | FS Seeds | HS32F50 | Enlist E3 | - | 9.2 | - | 82.6 | 82.6 |
+| 16 | FS Seeds | HS33E50 | Enlist E3 | - | 9.4 | - | 82.6 | 82.6 |
+| 18 | Asgrow | AG30XF4 | XTENDFlex | - | 9.3 | - | 82.4 | 82.4 |
+| 19 | Brevant Seeds | B294EE | Enlist E3 | - | 9.4 | - | 82.1 | 82.1 |
+| 20 | AgriGold | G2425E3 | - | - | 9.8 | - | 80.7 | 80.7 |
+| 21 | NK Brand | NK32-P2XF | XTENDFlex | - | 9.4 | - | 80.5 | 80.5 |
+| 21 | AgriGold | G2601E3 | Enlist E3 | - | 9.6 | - | 80.5 | 80.5 |
+| 23 | Asgrow | AG33XF3 | XTENDFlex | - | 9.2 | - | 80.2 | 80.2 |
+| 24 | AgriGold | G2755XF | XTENDFlex | - | 9.3 | - | 79.6 | 79.6 |
+| 25 | Asgrow | AG26XF4 | XTENDFlex | - | 9.7 | - | 79.4 | 79.4 |
+| 26 | FS Seeds | HS26F50 | XTENDFlex | - | 9.5 | - | 78.4 | 78.4 |
+| 27 | Asgrow | AG34XF6 | XTENDFlex | - | 9.4 | - | 78.0 | 78.0 |
+| 28 | AgriGold | G3255E3 | Enlist E3 | - | 9.4 | - | 77.0 | 77.0 |
+| 29 | Asgrow | AG32XF6 | XTENDFlex | - | 9.2 | - | 75.0 | 75.0 |
+| 30 | NK Brand | NK30-A9E3 | Enlist E3 | - | 9.6 | - | 74.8 | 74.8 |
+
+Top 5 by Yield: HS29F50 (FS Seeds) 90.5, B315EE (Brevant Seeds) 89.6, G2574XF (AgriGold) 87.3, B324EE (Brevant Seeds) 86.5, HS26E50 (FS Seeds) 85.9.