Stabilize civilian traffic by disabling RAT ATC and respawn churn

[bradyccox]

Summary

• Treat civilian_traffic as one-shot scenery instead of a repeating RAT traffic loop
• Disable RAT ATC broadcasts for civilian flights
• Stop civilian flights from respawning after landing to avoid the RAT_CIV_C130 crash path
• Update the in-game checklist and plugin docs to reflect the new behavior

Testing

• Not run (not requested)
• Validation rationale documented in the checklist: re-test civilian traffic during a Combat SAR pass and watch for any new RAT_CIV_* crash lead-up