Add mcp.json for VS Code when setting up

[tuanphuong-dev]

Description

Adds support for writing VS Code's native mcp.json file (introduced in VS Code 1.99) when running mimir setup, alongside the existing settings.json (Copilot) integration.

Changes

internal/setup/editors.go

• Added optional MimirEntry func() map[string]any field to the Editor struct, allowing per-editor customization of the MCP server entry format.
• Registered a new "VS Code (MCP)" editor entry targeting mcp.json:
  • macOS: ~/Library/Application Support/Code/User/mcp.json
  • Windows: %APPDATA%/Code/User/mcp.json
  • Linux: ~/.config/Code/User/mcp.json
  • Uses servers as the config key and MimirMCPEntryStdio as the entry generator.

internal/setup/mcp_writer.go

• Added MimirMCPEntryStdio() — generates an entry in the VS Code native format with "type": "stdio":

  {
    "type": "stdio",
    "command": "{path-to-mimir}",
    "args": ["mcp"]
  }