ci(integrations): add CI/CD workflows for n8n + Zapier packages

Match the repo's per-integration CI/CD convention (vercel-ai / pi-agent
pattern):

- n8n-nodes-mem0-checks.yml (lint + build + dist verify) and
  n8n-nodes-mem0-cd.yml (npm publish --provenance via OIDC, dispatched by
  the release router on tag n8n-nodes-mem0-v*).
- zapier-mem0-checks.yml (zapier validate) and zapier-mem0-cd.yml (manual
  zapier push; requires ZAPIER_DEPLOY_KEY). Zapier deploys to Zapier's
  platform, not npm, so it is not in the release router.
- Wire both packages into ci-gate.yml (path filters + call jobs + gate).
- Register the n8n tag prefix in release.yml and document it + the Zapier
  manual-deploy in AGENTS.md.
- Skip the Zapier E2E suite when MEM0_API_KEY is absent so CI is green
  offline (it still runs locally with a key).

.github/workflows/release.yml

@@ -45,6 +45,7 @@ jobs:
             openclaw-v*)  workflow="openclaw-cd.yml" ;;
             opencode-v*)  workflow="opencode-plugin-cd.yml" ;;
             pi-agent-v*)  workflow="pi-agent-plugin-cd.yml" ;;
+            n8n-nodes-mem0-v*) workflow="n8n-nodes-mem0-cd.yml" ;;
             v*)           workflow="cd.yml" ;;
             *)
               echo "::error::Release tag '$TAG' does not match any known package prefix — nothing will be published. See the tag prefix table in AGENTS.md."