feat(cockpit): ride the selected vessel from its bridge

With no aircraft tracked, Cockpit can ride the selected AIS vessel. Entry
needs only Live AIS Vessels and a selected vessel; C, double-click and the
entry buttons (reading BRIDGE with a ship icon) enter it, while voice stays
aircraft-only.

The eye sits on the AIS position at a representative bridge height for the
vessel's type family, looks along true heading and moves along course over
ground. The last fix is dead-reckoned for up to 180 s between the layer's
refreshes, and on rivers and lakes the waterline is read from the rendered
surface around the ship rather than the geoid.

The bridge HUD shows speed and course over ground, a straight heading
tape, window mullions, the AIS destination as a reported voyage and a
heading-up radar of nearby ships (3 to 24 NM). The arrow keys look around,
Home or 0 looks ahead again. The vessel layer hides the ridden ship's
sprite and card, ignores scene clicks while held, and returns the camera
to the vessel's map view on exit.

src/cockpitMath.test.mjs

@@ -11,6 +11,8 @@ import {
   cockpitSurfaceWaitExpired,
   cockpitUiUpdateDue,
   compassDivisions,
+  compassMarkerSlot,
+  scrollingCompassDivisions,
   formatAltitudeRulerTick,
   formatCockpitContextScope,
   formatCockpitEmergency,
@@ -151,6 +153,46 @@ test('compass divisions remain ordered across north', () => {
   assert.deepEqual(compassDivisions(359), [270, 300, 330, 0, 30, 60, 90]);
 });
 
+test('compass marks sit in division slots off the caret, or off the tape', () => {
+  // Measured from the exact heading under the caret, not the nearest division.
+  assert.equal(compassMarkerSlot(350, 350), 0);
+  assert.equal(compassMarkerSlot(35, 350), 1.5);
+  assert.equal(compassMarkerSlot(260, 350), -3);
+  assert.equal(compassMarkerSlot(80, 350), 3);
+  assert.equal(compassMarkerSlot(90, 350), null);
+  assert.equal(compassMarkerSlot(180, 350), null);
+  assert.equal(compassMarkerSlot(Number.NaN, 0), null);
+});
+
+test('a scrolling tape puts the exact heading under the caret', () => {
+  // At 100° the divisions sit a third of a slot off their snapped places,
+  // so the bow mark (also 100°) lines up with the caret, not 10° beside it.
+  const tape = scrollingCompassDivisions(100);
+  assert.deepEqual(
+    tape.map(({ heading }) => heading),
+    [330, 0, 30, 60, 90, 120, 150, 180, 210],
+  );
+  const nearest = tape.find((division) => division.nearest);
+  assert.equal(nearest.heading, 90);
+  assert.equal(nearest.slot, -0.3333);
+  assert.equal(tape.find(({ heading }) => heading === 120).slot, 0.6667);
+  assert.equal(compassMarkerSlot(100, 100), 0);
+  assert.equal(compassMarkerSlot(90, 100), nearest.slot);
+  // Across north the slots stay continuous.
+  assert.deepEqual(
+    scrollingCompassDivisions(355, 1).map(({ heading, slot }) => [
+      heading,
+      slot,
+    ]),
+    [
+      [330, -0.8333],
+      [0, 0.1667],
+      [30, 1.1667],
+    ],
+  );
+  assert.deepEqual(scrollingCompassDivisions(Number.NaN), []);
+});
+
 test('compass labels use cardinals where exact and degrees elsewhere', () => {
   assert.equal(formatCompassDivision(270), 'W');
   assert.equal(formatCompassDivision(30), '030');