- Modified handle_zoom_threshold_crossing to detect tracked_callsign
- Show trail line instead of heat map when tracking at zoom ≤ 8
- Maintain heat map behavior when not tracking
- Maintain marker behavior at zoom > 8
- Filters packets by tracked callsign and time threshold
- Sorts packets chronologically by received_at
- Pushes show_trail_line event with coordinates
- Returns socket unchanged when no packets found
