docs: add PZERO as a remote streamable-http MCP example

[cursor]

Please add PZERO as a remote MCP example next to the GitHub / PayPal snippets in https://www.librechat.ai/docs/features/mcp

PZERO is hosted inference over Model Context Protocol (chat, image, video). Auth is a Bearer pzero_… API key, same shape as GitHub PAT. Official registry: studio.pzero/mcp. Docs: https://docs.pzero.studio/agents/mcp

Suggested librechat.yaml block (mirrors the GitHub PAT example):

mcpServers:
  pzero:
    type: streamable-http
    url: 'https://mcp.pzero.studio/mcp'
    headers:
      Authorization: 'Bearer {{PZERO_API_KEY}}'
    customUserVars:
      PZERO_API_KEY:
        title: 'PZERO API key'
        description: 'pzero_… key from https://pzero.studio/agents after you top up'
    startup: false

Fund at https://pzero.studio/agents (min top-up 1 USDC on Base). MCP does not run x402 itself.

Happy to tweak names if you prefer requiresOAuth: false spelled out.