feat(integrations): add n8n community node for Mem0

Programmatic n8n node (n8n-nodes-mem0) with Add/Search/Get Many/Get/
Update/Delete memory operations against the Mem0 v3 API, plus API-key
credentials and usableAsTool support for the AI Agent node.

Add uses POST /v3/memories/add/ and polls GET /v1/event/{id}/ until the
async extraction resolves. No runtime dependencies (n8n verification
requirement); calls the REST API directly. MIT licensed per-package.

integrations/n8n-nodes-mem0/index.js

@@ -0,0 +1,3 @@
+// n8n loads nodes and credentials via the "n8n" key in package.json.
+// This entry point is intentionally empty.
+module.exports = {};