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-2024-144536.md

@@ -0,0 +1,52 @@
+# Soybean yield trial — Whitewater, KS, 2024
+
+- **Source:** AgriGold plot report (cross-vendor head-to-head)
+- **Vendor:** AgReliant Genetics / AgriGold
+- **Crop:** Soybean
+- **State:** KS
+- **County:** Butler
+- **City:** Whitewater
+- **Year:** 2024
+- **Plot ID:** 144536
+- **Cooperator:** The Feedstore
+- **Plot average:** 52.22 BU/Ac
+- **Planted:** 2024-06-14
+- **Harvested:** 2024-10-23
+- **Population:** 120,000 seeds/acre
+- **Row width:** 30.0"
+- **# Rows:** 5
+- **Tillage:** No Till
+- **Previous crop:** Corn
+- **Irrigation:** None
+- **URL:** https://www.agrigold.com/soybeans/performance/soybean-yield-results/144536
+
+---
+## Results (by rank)
+
+| Rank | Brand | Product | Trait | Ck | H20 | Test Wt. | Yield | Adj Yield |
+|---|---|---|---|---|---|---|---|---|
+| 13 | NC+ | F4151 | XTENDFlex | - | 7.1 | 59.2 | 50.9 | 50.9 |
+| - | AgriGold | G4615XF | XTENDFlex | - | 7.3 | 57.7 | 49.2 | 49.2 |
+| 18 | AgriGold | G4094XF | XTENDFlex | - | 7.0 | 59.2 | 47.5 | 47.5 |
+| 15 | AgriGold | G4184XF | XTENDFlex | - | 7.2 | 58.5 | 49.8 | 49.8 |
+| 16 | AgriGold | G4204E3 | Enlist E3 | - | 6.8 | 59.8 | 49.6 | 49.6 |
+| 17 | NC+ | E4131S | Enlist/STS | - | 7.1 | 59.0 | 48.4 | 48.4 |
+| - | AgriGold | G4615XF | XTENDFlex | - | 7.1 | 59.8 | 52.9 | 52.9 |
+| 11 | Hoegemeyer | 4234E | Enlist E3 | - | 7.4 | 58.2 | 51.6 | 51.6 |
+| 12 | AgriGold | G4430XF | XTENDFlex | - | 7.1 | 59.4 | 51.1 | 51.1 |
+| 2 | NC+ | NC44F52S | XTENDFlex/STS | - | 7.4 | 59.5 | 55.1 | 55.1 |
+| 14 | NC+ | E4531S | Enlist/STS | - | 7.4 | 58.9 | 50.1 | 50.1 |
+| - | AgriGold | G4615XF | XTENDFlex | - | 7.6 | 58.5 | 52.3 | 52.3 |
+| 8 | Hoegemeyer | 4355BE | Enlist E3 | - | 7.5 | 59.0 | 53.2 | 53.2 |
+| 10 | Ohlde Seed | O2146E | Enlist E3 | - | 7.7 | 58.0 | 51.7 | 51.7 |
+| 1 | Hoegemeyer | 4385E | Enlist E3 | - | 7.2 | 56.8 | 55.5 | 55.5 |
+| 5 | Hoegemeyer | 4525E | Enlist E3 | - | 7.5 | 57.1 | 54.9 | 54.9 |
+| 2 | AgriGold | G4615XF | XTENDFlex | - | 7.4 | 59.6 | 55.1 | 55.1 |
+| - | AgriGold | G4615XF | XTENDFlex | - | 7.4 | 59.6 | 55.1 | 55.1 |
+| 4 | Hoegemeyer | 4743E | Enlist E3 | - | 7.7 | 58.9 | 54.9 | 54.9 |
+| 9 | Hoegemeyer | 4785E | Enlist E3 | - | 7.5 | 59.4 | 52.8 | 52.8 |
+| 6 | AgriGold | G4884E3 | Enlist E3 | - | 7.5 | 58.9 | 54.2 | 54.2 |
+| 7 | NC+ | NC48F54S | XTENDFlex/STS | - | 8.6 | 57.6 | 53.6 | 53.6 |
+| - | AgriGold | G4615XF | XTENDFlex | - | 7.4 | 58.7 | 47.0 | 47.0 |
+
+Top 5 by Yield: 4385E (Hoegemeyer) 55.5, NC44F52S (NC+) 55.1, G4615XF (AgriGold) 55.1, G4615XF (AgriGold) 55.1, 4525E (Hoegemeyer) 54.9.