Show direction-of-flight arrows on aircraft track lines

Problem:

When viewing aircraft tracks on the map, there is no visual indicator of which direction the aircraft was (or is) travelling, reducing situational awareness.

Desired outcome:

Users can immediately see the direction of flight on any track line without needing to inspect individual points.

Proposed change:

Add direction arrow markers (chevrons/barbs) along each aircraft track polyline, controlled by a new "Direction Arrows" toggle in Track Display options.