mcp: init module

[delafthi]

This PR adds a new mcp module that provides unified configuration management for Model Context
Protocol (MCP) servers. Instead of duplicating server definitions across multiple tools, users can define MCP servers once in programs.mcp.servers and optionally enable tool-specific integrations.

The module currently generates the standard ~/.config/mcp/mcp.json configuration file and includes an enableOpencodeIntegration option that automatically translates the MCP server definitions into OpenCode's configuration format.

Future Integrations

The design allows for additional tool integrations to be added following the same pattern:

• enableVscodeIntegration - for Visual Studio Code
• Any other tools that support MCP servers

Each integration would translate programs.mcp.servers into the respective tool's configuration format, maintaining a single source of truth for MCP server definitions.

Checklist

• Change is backwards compatible.

• Code formatted with nix fmt or
  nix-shell -p treefmt nixfmt deadnix keep-sorted --run treefmt.

• Code tested through nix run .#tests -- test-all or
  nix-shell --pure tests -A run.all.

• Test cases updated/added. See example.

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module

  • Added myself as module maintainer. See example.
  • Generate a news entry. See News
  • Basic tests added. See Tests

• If this PR adds an exciting new feature or contains a breaking change.

  • Generate a news entry. See News

[khaneliman]

Thanks, brief glance looks good. I'll take a detailed look a little bit later.

[khaneliman]

Sorry, could you move the vscode and opencode changes to their own respective commits. So, we have a commit that introduced the mcp module and then commits for vscode/opencode adding their integrations with it.

Would also be nice to have a news entry for the new module and functionality