Fix auto-close setup and lifetime bounds

[TeoSlayer]

What changed

• give relay/session setup its own signal-bound context instead of spending the process auto-close budget
• start relative durations when the wrapped process is ready to launch
• preserve absolute wall-clock deadlines
• clamp explicit deadlines to the relay's returned expiry so cards, JSON, and shell list stay truthful
• add regression coverage for sub-second, absolute, and overlong deadlines

Test

• go test ./...

Closes #18
Closes #19