terminal-pet: the second TUI face #11

Nothing renders keys_per_min, session_seconds, or any of the five hardware signals. The pet is their consumer, which also makes the supervision work observable.

Stateless: a pure function of the current snapshot. No persistence, no animation timeline, no config.

Done when:

• crates/terminal-pet/ mirrors the garden's split: lib.rs holds signals -> PetState -> render with unit tests, main.rs is the subscribe loop.
• Energy from KeysPerMin, stress from ThermalState and CpuLoad, condition from BatteryPct and Charging.
• Any CollectorUp at 0.0 renders sick, overriding the rest; a signal whose ts is more than 30s old renders dimmed.