[FabioHAraujo]

Builds on #113 and #114: merge those first. Until then this diff also shows their commits. This PR itself changes only Markdown.

Documentation for the MCP server

• docs/MCP.md (new) is the user guide. It covers:
  • turning the server on and sharing vaults;
  • configuration for Claude Desktop, Claude Code and Cursor, and where lownotes-mcp lives on each system (and why the AppImage does not work);
  • the five tools and the note resource;
  • what leaves LowNotes, prompt injection from synced notes, who can connect, regenerating the token, and what the log records;
  • troubleshooting by the bridge's error messages.
• docs/THREAT-MODEL.md:
  • the MCP token is listed as an asset;
  • a new section covers local MCP clients and their models: off by default, read-only, only shared vaults, the per-user pipe DACL and Unix socket permissions, the token in the credential store, the check that the pipe's server runs as the same user, request limits, data reaching the client's provider, prompt injection, and logging;
  • two new known limits: a client with other tools can be steered by injected text, and any process of the same user can read the token from the credential store.
• docs/ARCHITECTURE.md:
  • rows for vault_service.rs and the MCP modules;
  • the server's threads (Tauri async runtime, tool calls on the blocking pool, restarts that wait for the endpoint) and the bridge process, which never opens the vault;
  • the token and the socket in the data table.
• README.md: a "Bring your own AI app" line and an "AI apps over MCP" section that links to the guide.
• CHANGELOG.md: one entry under [Unreleased] → Added covering MCP server inside the app with read-only tools over a local pipe or socket #101–Document the MCP server in the threat model, architecture and a user guide #104. No version section.

Relative links were checked. The full AGENTS.md verification ran on #114's tree, which this branch only extends with Markdown.

Closes #104