fix: deliver background results before exit

[zerone0x]

Summary

• keep the s08 background loop alive long enough to inject late background results
• wait for running tasks and wake the loop when results enqueue
• avoid dropping notifications after an end_turn response

Fixes #46

Testing

• not run (logic-only change)

[vercel]

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[zerone0x]

closing as duplicate of #149, which already addresses the background notification issue