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/cockpitMath.test.mjs

@@ -161,6 +161,7 @@ test('a heading that rounds to north reads 000, not 360', () => {
   assert.equal(formatHeadingReadout(359.4), '359');
   assert.equal(formatHeadingReadout(0), '000');
   assert.equal(formatHeadingReadout(10.2), '010');
+  assert.equal(formatHeadingReadout(-0.6), '359');
   assert.equal(formatHeadingReadout(Number.NaN), '---');
 });