fix(cockpit): read a rounded-north destination heading as 000

359.6 degrees was shown as 360 degrees on the destination bearing while the compass tape uses 000.

src/cockpitMath.test.mjs

@@ -15,6 +15,7 @@ import {
   formatCockpitContextScope,
   formatCockpitEmergency,
   formatCompassDivision,
+  formatHeadingReadout,
   formatSpeedRulerTick,
   normalizeHeading,
   relativeBearing,
@@ -155,6 +156,14 @@ test('compass labels use cardinals where exact and degrees elsewhere', () => {
   assert.equal(formatCompassDivision(30), '030');
 });
 
+test('a heading that rounds to north reads 000, not 360', () => {
+  assert.equal(formatHeadingReadout(359.6), '000');
+  assert.equal(formatHeadingReadout(359.4), '359');
+  assert.equal(formatHeadingReadout(0), '000');
+  assert.equal(formatHeadingReadout(10.2), '010');
+  assert.equal(formatHeadingReadout(Number.NaN), '---');
+});
+
 test('great-circle bearing resolves cardinal directions', () => {
   assert.ok(Math.abs(bearingBetweenCoordinates(0, 0, 1, 0) - 0) < 0.001);
   assert.ok(Math.abs(bearingBetweenCoordinates(0, 0, 0, 1) - 90) < 0.001);