Add an EXIT trap in entrypoint-reproduce.sh that:
- Switches back to the primary branch
- Deletes the triage-debug-${ISSUE_NUMBER} branch
This ensures the throwaway branch used for debug instrumentation
(console.log, verbose logging) is cleaned up if the agent crashes
or times out, preventing repository pollution.
The trap is combined with existing cleanup (heartbeat kill, stack
lock release) into a single EXIT handler.
