Implement Samsung FridgeOS-themed shell (PLAN.md §3.3) with inventory
management, temperature controls, diagnostics, alerts, and other
appliance commands. Add per-credential shell routing so static
credentials can specify which shell to use via the `shell` config field,
passed through ssh.Permissions.Extensions.
Also extract shared ReadLine helper from bash to the shell package so
both shells can reuse terminal input handling.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
