Round every heading readout through one shared helper

The transit, ALPR, vessel, CCTV and flight/military context fixes each
wrapped 359.5° to north with an inline Math.round(x) % 360. They now call
roundHeadingDegrees in src/data/headingDegrees.js, which also wraps negative
and multi-turn bearings. normalizeHeading moves there with it, and
cockpitMath re-exports it so existing imports keep working. It now adds a
turn only to a negative remainder, so a bearing just under half a degree
keeps its precision.

The awareness, Local ADS-B, cockpit wind, cockpit heading and Street Level
readouts use the same helper. The Cockpit's TRACK ACQUIRED signal rounded
without wrapping and could read COURSE 360°; it now uses
formatHeadingReadout, which shows --- for a track that is not finite.

src/ui/cockpitInstruments.js

@@ -120,7 +120,7 @@ export function updateHud(
     (tick) => formatAltitudeRulerTick(tick.valueFt),
   );
   view.heading = {
-    text: String(Math.round(heading) % 360).padStart(3, '0'),
+    text: formatHeadingReadout(heading),
     value: heading,
     immediate: forceContext,
   };