MCP interactive wizard lacks help text for environment variable format

[loganrosen]

Describe the bug

When using /mcp add to interactively add an MCP server, the Environment Variables field only shows:

Environment Variables: Path is automatically inherited. All other environment variables must be configured

This tells users that environment variables need to be configured, but does not explain how to define them — there is no indication of the expected input format (e.g., KEY=VALUE, JSON, one per line, comma-separated, etc.). Users are left to guess or look up external documentation.

Other fields in the wizard include clearer guidance (e.g., the Tools field says use "*" for all tools), but the Environment Variables field lacks equivalent formatting instructions.

Steps to reproduce the behavior

1. Start copilot
2. Execute /mcp add
3. Select STDIO as the server type
4. Observe the "Environment Variables" input field — the help text explains that env vars must be configured but does not explain the expected format for entering them

Expected behavior

The Environment Variables field should include help text or a placeholder indicating the expected input format (e.g., KEY=VALUE, one per line or similar), so users know how to define variables without trial and error.