render_report_telegram_summary (pure, no new deps, DRY-reuses report_pdf str
helpers) + `tg` format on GET /{cad}/forecast/export → inline text/plain snippet
(no attachment, copy-paste-ready). md/json unchanged; no-run 404, bad format 422.
Graceful on thin/empty reports. Part of EPIC #959.
render_report_markdown (pure, no new runtime deps) reuses report_pdf's str
helpers (DRY), + GET /{cad_num}/forecast/export?format=md|json. No forecast run
→ 404; graceful on thin/empty reports; GFM-safe table escaping. PDF/XLSX already
existed; this adds the cheapest no-dep formats. Part of EPIC #959.
