docs(integrations): add Zapier and n8n docs; align n8n toolchain and codex

- Add docs/integrations/zapier.mdx and n8n.mdx, register both in docs.json
  (Developer Tools) and docs/llms.txt
- Align n8n CD toolchain (pnpm 9 / Node 20) with the checks workflow so the
  published artifact is built on the toolchain CI validated
- Add Mem0.node.json codex and copy it into dist via gulp for nodes-panel
  discoverability
- Align search default limit to 50 across Zapier and n8n

integrations/zapier-mem0/searches/search_memories.js

@@ -4,7 +4,7 @@ const perform = async (z, bundle) => {
 	const body = {
 		query: bundle.inputData.query,
 		output_format: 'v1.1',
-		top_k: Math.max(1, Math.floor(Number(bundle.inputData.limit) || 10)),
+		top_k: Math.max(1, Math.floor(Number(bundle.inputData.limit) || 50)),
 	};
 	if (bundle.inputData.user_id) body.filters = { user_id: bundle.inputData.user_id };
 
@@ -30,7 +30,7 @@ module.exports = {
 		inputFields: [
 			{ key: 'query', label: 'Query', type: 'string', required: true },
 			{ key: 'user_id', label: 'User ID', type: 'string', required: true },
-			{ key: 'limit', label: 'Limit', type: 'integer', default: '10' },
+			{ key: 'limit', label: 'Limit', type: 'integer', default: '50' },
 		],
 		sample: { id: '00000000-0000-0000-0000-000000000000', memory: 'User loves hiking' },
 	},