Fix render loop that was dispatching DELIVER_PASSENGER hundreds of times
per second when train remained at station, causing:
- Train stoppage despite correct answers
- Violent flashing in passenger HUD list
- Server rejecting moves: "Player does not have this passenger"
Solution:
- Add pendingDeliveryRef to track passengers with pending deliveries
- Check if delivery already dispatched before dispatching again
- Mark passenger as pending immediately before dispatch
- Clean up pending set when passengers are delivered
- Clear pending set on route changes
This mirrors the existing pendingBoardingRef pattern used for boarding.
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Co-Authored-By: Claude <noreply@anthropic.com>
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