Bring terminal CLI slash commands to the Claude Code app

The app version of Claude Code is missing many built-in slash commands available in the terminal CLI (/status, /compact, /clear, /diff, /config, etc.). Users coming from the terminal experience expect these to be available. The app adds great new capabilities (MCP, browser automation, scheduled tasks) but losing core CLI commands feels like a downgrade.

Request: Port the terminal CLI slash commands to the app version so the experience is consistent across both clients.