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

docs/llms.txt

@@ -281,6 +281,8 @@ If the user is on a pre-current major (Python < 2, TS < 3, or Platform `output_f
 ### Developer Tools
 - [Dify](https://docs.mem0.ai/integrations/dify) [Both]: Use when the user is on Dify LLMOps.
 - [Flowise](https://docs.mem0.ai/integrations/flowise) [Both]: Use when the user is on Flowise no-code.
+- [n8n](https://docs.mem0.ai/integrations/n8n) [Both]: Use when the user builds workflows or AI agents in n8n.
+- [Zapier](https://docs.mem0.ai/integrations/zapier) [Both]: Use when the user automates workflows with Zapier.
 - [AgentOps](https://docs.mem0.ai/integrations/agentops) [Both]: Use when tracking agent observability with memory metadata.
 - [Respan](https://docs.mem0.ai/integrations/respan) [Both]: Use when monitoring Mem0 with Respan (formerly Keywords AI) LLM observability.
 - [Raycast](https://docs.mem0.ai/integrations/raycast) [Both]: Use when the user wants quick memory access via Raycast.