feat(typescript-recipes): add parallel-procurement-n8n recipe

[s-jag]

Summary

Adds a new recipe under typescript-recipes/parallel-procurement-n8n/ — continuous vendor risk monitoring built on the Parallel Task and Monitor APIs, orchestrated by n8n, with Slack-routed alerts and a cited audit log. Slots into the Scheduled Research & Webhooks category next to parallel-daily-insights.

What's in the recipe:

• One combined n8n workflow (50 nodes) covering vendor sync (every 6h), daily Deep Research via Task Groups, V1 event-stream monitors, deterministic risk scoring, severity routing into Slack, and an ad-hoc /vendor-research slash command.
• output.basis lift-through — every assessment and Slack alert carries the top citation per dimension, and the audit log writes top_citation_url / top_citation_title / confidence per row.
• 46 Vitest suites (629 tests) — services, models, workflow JSON structure, full pipeline integration, vendor lifecycle, nine error scenarios, scale simulation (200 / 3000 vendors).
• Optional Next.js + Supabase BYOK dashboard reimplementing the same business logic for users who would rather not run n8n. Includes one-click Vercel deploy in DEPLOY.md.

Registered in both indexes per CONTRIBUTING.md:

• Row in README.md under Scheduled Research & Webhooks.
• Entry in website/cookbook.json (slug parallel-procurement-n8n).

Why draft

Submitting as draft because a few items from the cookbook quality bar are still TODO:

• Live demo URL — n8n side is self-hosted; will record a Loom walkthrough and patch in. Dashboard one-click Vercel deploy is wired but not hosted at a public URL yet.
• Architecture diagram as PNG — four Excalidraw sources ship today (system-architecture.excalidraw and friends); will export a PNG into docs/ for the README.
• creators field in cookbook.json — currently ["sahith-3694"]; tell me if it should be a different handle.
• Category decision — slotted under Scheduled Research & Webhooks. Happy to move it or create a new Workflow Automation category if preferred.

PR Checklist (CONTRIBUTING.md)

• Recipe runs end-to-end from a fresh clone using only the README (npm ci && npm test → 629 passed)
• Live demo URL is reachable — see "Why draft"
• No API keys, secrets, or .env / .dev.vars committed — pre-commit run passes (detect-private-key, gitleaks, forbid-env-files)
• No hardcoded infra IDs — n8n workflow JSON uses \$vars.PARALLEL_API_KEY and {{ \$env.SLACK_WEBHOOK_URL }} placeholders; dashboard reads everything from env
• Production-only routes properly isolated (Vercel cron in dashboard/vercel.json)
• Lockfiles committed (package-lock.json at root and in dashboard/)
• LICENSE included (MIT, copyright (c) 2026 Shapley AI, Inc.)
• Title and description fit on one line each
• Recipe added to both README.md and website/cookbook.json

Test plan

• CI passes (pre-commit + any per-recipe jobs)
• Reviewer sanity-checks the README.md table row and cookbook.json entry against cookbook.schema.json
• Reviewer optionally runs npm ci && npm test inside typescript-recipes/parallel-procurement-n8n/