fix(flight-data): scale bearing vectors with map

[obazna]

Summary

• Treat the configured Flight Data bearing-line length as a map distance in metres.
• Let heading, navigation, course and target vectors shrink naturally when zooming out.
• Remove the superseded viewport-resolution callback and cached MAV state.
• Label the Planner setting as Line Length (m).
• Add a regression covering both interactive zoom and the following telemetry redraw.

Why

Live validation showed that upstream-style constant screen-pixel vectors are unsuitable in the Avalonia map: the default 500-pixel lines span countries at regional and world zoom. This change deliberately uses stable map-distance vectors instead.

With a configured 500m vector, the regression verifies 250px at resolution 2, 62.5px after zooming to resolution 8, and 62.5px after the next vehicle redraw.

Verification

• FlightMapOverlayTests: 29/29 passed
• Release build: 0 warnings, 0 errors
• Complete local suite: 1566/1567 passed; only the existing host-sensitive /dev/video0 normalization case failed
• Behavior, integration and test reviewers approved exact head b5a8dfa

Manual acceptance

Rebuild and relaunch this branch, connect a live vehicle, then zoom Flight Data to a regional or world view. Bearing vectors should stay local to the aircraft and shrink with the map, with no duplicated aircraft symbols.