Remove Herd MCP integration in favor of Herd CLI

[pushpak1300]

Herd 1.26.0 introduced CLI commands that replace the functionality previously provided by the Herd MCP server. The herd CLI now supports service management, PHP version management, site listing, secure/unsecure, and isolate/unisolate — making the separate MCP integration unnecessary.

Approach

• Removed the Herd MCP installation prompt, config, and writer logic from the install command
• Removed isMcpAvailable() and mcpPath() from the Herd class (kept isInstalled() for guideline/prompt use)
• Updated the Herd guideline to document the equivalent herd CLI commands
• Removed related tests and added a sail + nightwatch combo test

Warning

The herd_mcp config key in boost.json is no longer read or written. Existing projects with this key set will simply ignore it on next install.