Add MCP tools for Xdebug toggle #76

Problem

Local supports enabling/disabling Xdebug per site through its UI. Useful when the agent is debugging a hairy bug and wants to suggest the user attach a debugger — currently requires manual UI clicks to flip Xdebug on/off.

Proposal

• enable_xdebug(siteId?)
• disable_xdebug(siteId?)
• get_xdebug_status(siteId?) → current state plus connection info (host, port, IDE key)

LocalApi additions

LocalApi.enableXdebug, disableXdebug, getXdebugStatus.

Acceptance criteria

• State persists across site restarts
• Status tool returns useful info (port, IDE key) for configuring an IDE
• Errors clearly when site is halted