Optional MCP server wrapper so MCP agents can use Mnemonic without the HTTP client

[omarnagy91]

Mnemonic exposes an HTTP API. An optional MCP (Model Context Protocol) server wrapping add / search / context / reflect as tools would let MCP-speaking agents (Claude Desktop, Claude Code, others) use it directly.

Scope: a thin MCP server that calls the existing routes; no change to the core. Document how to register it.

Acceptance: an MCP server exposing at least add and search/context as tools, with setup docs. Keep it optional and out of the core dependency set.