fix: stop containers on Ctrl-C and add SIGTERM handler

[Jaro-c]

Problem

1. LIFE-003: Ctrl-C during podup up exits attach_logs (which catches SIGINT) but leaves all containers running — orphaned indefinitely.
2. SIG-001: No SIGTERM handler. Sending SIGTERM to the process has no effect; containers are never cleaned up.

Fix

After attach_logs returns (whether by Ctrl-C, SIGTERM, or streams ending), call engine.stop() to perform an ordered shutdown of all containers.

Add a unified signal handler that catches both SIGINT and SIGTERM and triggers the same shutdown path.