feat: viz mcp aggregator

[snehshah22]

Description

This PR refactors the MCP server to support dual proxy aggregation, connecting to both Notebook and Visualization MCP sockets simultaneously. It transitions the server from a single-proxy pass-through model to a master-aggregator architecture.

Key Changes

Directory Structure

• Renamed notebook_mcp/ to mcp/ to reflect its expanded role as a multi-domain aggregator.
• Updated root package.json and release-please-config.json to point to the new mcp/ directory.

MCP Server (mcp/server.ts)

• Refactored server.ts to act as a master MCP server.
• Added logic to spawn and connect to both notebooks-[ide_name] and visualization-[ide_name] proxies using StdioClientTransport.
• Implemented tool list aggregation: ListToolsRequestSchema handler merges tools from both proxies.
• Implemented request routing: CallToolRequestSchema routes tool calls to the correct underlying proxy based on a tool ownership map.
• Implemented resilient fallback logic:
  • If both proxies fail, it falls back to standalone mode serving local tools.
  • If one proxy fails, it still provides tools from the successful proxy and falls back to local tools for the failed domain if applicable.
• Fixed a bug where failed client connections were not reset to null, preventing correct fallback behavior.

Build and Dependencies

• Updated mcp/build.js to treat cross-spawn and Node.js built-ins as external modules to avoid dynamic require errors in ESM output.
• Added cross-spawn as an explicit dependency in the root package.json to ensure it is available when running via npx from the git repository.