feat(globe): mover sets report ready(); Navara scales by distance as Cesium

Task 10b foundation.
- MoverSet.ready(): whether what the set draws has loaded (Navara: the
  model set's glTF, a URL atlas; Cesium: every instance's Model, the cropped
  atlas; parts without it draw at once). The aircraft renderer keeps the 2D
  glyph until a model set is ready, as the Cesium path waits on Model.ready.
  Contract suite: a drawn model set is ready() (both engines); unit test of
  the neutral store.
- Navara sprites and points interpolate scaleByDistance as Cesium's
  NearFarScalar (over the squared camera distance, eased by ^0.2) instead
  of linearly in distance, so aircraft glyphs have Cesium's size at every
  range; the CPU pick radius follows (distanceScale, tested equal to
  focusDeemphasis' port of czm_nearFarScalar). The contract text says so.

src/globe/cpuPicks.test.mjs

@@ -46,8 +46,28 @@ test('the CPU pick radius follows scaleByDistance', () => {
   const shrink = [1_000, 1, 10_000, 0.25];
   assert.equal(pickAt(22, shrink), 0);
   assert.equal(pickAt(7, shrink), 1);
-  // Halfway between near and far: linear, as the Navara shader draws it.
+  // Halfway between near and far: Cesium's NearFarScalar (squared distance,
+  // eased by ^0.2): t = 0.25^0.2 = 0.758, scale 0.621, radius 12.4 + 3 px.
   const half = [0, 1, 20_000, 0.5];
-  assert.equal(pickAt(17, half), 1, '15 + 3 px');
-  assert.equal(pickAt(19, half), 0);
+  assert.equal(pickAt(15, half), 1, '12.4 + 3 px');
+  assert.equal(pickAt(16, half), 0);
+});
+
+test('distanceScale is Cesium.NearFarScalar interpolation', async () => {
+  const Cesium = await import('cesium');
+  const { distanceScale } = await import('./cpuPicks.js');
+  const scalar = [1000, 3.0, 8_000_000, 0.5];
+  // Cesium's czm_nearFarScalar on the CPU (focusDeemphasis ports it too).
+  const { nearFarScalarValueAtDistance } =
+    await import('../data/focusDeemphasis.js');
+  for (const distance of [0, 1000, 5000, 1e5, 2e6, 8e6, 2e7]) {
+    const expected = nearFarScalarValueAtDistance(
+      new Cesium.NearFarScalar(...scalar),
+      distance,
+    );
+    assert.ok(
+      Math.abs(distanceScale(scalar, distance) - expected) < 1e-12,
+      `${distance} m`,
+    );
+  }
 });