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/n8n-nodes-mem0/nodes/Mem0/Mem0.node.json

@@ -0,0 +1,21 @@
+{
+	"node": "n8n-nodes-mem0.mem0",
+	"nodeVersion": "1.0",
+	"codexVersion": "1.0",
+	"categories": ["AI"],
+	"subcategories": {
+		"AI": ["Memory"]
+	},
+	"resources": {
+		"primaryDocumentation": [
+			{
+				"url": "https://docs.mem0.ai/integrations/n8n"
+			}
+		],
+		"credentialDocumentation": [
+			{
+				"url": "https://docs.mem0.ai/integrations/n8n"
+			}
+		]
+	}
+}