Update MCP docs with security info

[Steve-Mcl]

Description

• https://flowfuse.com/blog/2025/10/building-mcp-server-using-flowfuse/#prerequisites
• https://flowfuse.com/node-red/flowfuse/mcp/

We had a support ticket recently where a user was trying connect via VSCode to secured MCP server nodes. They followed the blog post and could not connect. Our article and our docs do not mention the node security or creating a FlowFuse token or how to use it.

Epic/Story

No response

Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate