Add label and last-seen sorting to the devices command

[jongio]

The devices command can sort by health, but users with many probes also need stable inventory views for setup, labeling, and troubleshooting.

Acceptance criteria:

• thermoworks devices --sort label sorts by display label, falling back to serial.
• thermoworks devices --sort last-seen shows newest devices first.
• Existing --sort health behavior keeps working.
• Tests cover parsing and ordering.