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.

rag/chunk.py

@@ -509,6 +509,28 @@ def _render_trial_chunk(sidecar: dict, md_text: str | None = None) -> str:
     # for each (Golden Harvest / LG Seeds / AgriGold).
     if source in ("gh_plot_reports", "lg_plot_reports", "agrigold_plot_reports"):
         return _render_gh_plot_chunk(sidecar)
+    if source == "proharvest_plots":
+        # Structured rows → shared cross-vendor renderer (publisher brand
+        # read from the sidecar). Foreign-format third-party PDFs that
+        # couldn't be parsed into rows carry raw_text=True and the verbatim
+        # table text in the .md body — embed that so they're still found.
+        if sidecar.get("results"):
+            return _render_gh_plot_chunk(sidecar)
+        crop = (sidecar.get("crop") or "").lower()
+        crop_label = {"corn": "Corn", "soybeans": "Soybean"}.get(crop, crop.title())
+        coop = sidecar.get("cooperator") or ""
+        state = sidecar.get("state") or ""
+        year = sidecar.get("year") or ""
+        head = [
+            f"# {crop_label} yield trial — {coop} ({state}, {year})", "",
+            "ProHarvest Seeds plot report (cross-vendor, verbatim from PDF).", "",
+        ]
+        body = md_text or ""
+        sep = "## Trial data (verbatim from PDF)"
+        if sep in body:
+            body = body.split(sep, 1)[1].strip()
+            body = re.sub(r"```", "", body).strip()
+        return "\n".join(head) + "\n" + body + "\n"
     if source == "agripro_trials":
         header = _render_agripro_trial_chunk(sidecar)
         if md_text: