fix(street-level): camera height over Google 3D, cast only when it helps, gate token

From the code review of #768:

- view.js measured the camera's height above ground with globe.getHeight,
  but Google 3D hides the globe, so coverage picked its zoom from the
  ellipsoidal height. Over a high city (Denver, ~1,600 m) a camera 500 m up
  read 2,100 m: coverage stayed at z12/z13, whose tiles are too big to cast,
  and lines stayed draped on the roofs. With the globe hidden, the bare-earth
  height from the ground caster now answers; coverage re-picks its zoom when
  the surface mode changes. Verified in Denver: terrain mode, z14, cast lines.
  The core's surface check uses the same helper (and no longer subtracts the
  2 m lift from the camera height).
- castTile rebuilt a tile even when no line could be cast (terrain proxy
  down, tile too big); it now leaves such tiles as they are.
- The feature gate read Street Level's share token as a literal `0`; it now
  takes it from LAYER_STATE_REGISTRY, since a rebase can reassign it.

New view.test.mjs covers the shown-globe, hidden-globe and no-sample cases.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/layers/streetLevel/view.test.mjs

@@ -0,0 +1,44 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { cameraHeightAboveGround } from './view.js';
+
+const RAD = Math.PI / 180;
+/** A viewer 300 m above a street 1,600 m up (Denver-like). */
+function viewer({ globeShown, globeHeight }) {
+  return {
+    camera: {
+      positionCartographic: {
+        longitude: -104.99 * RAD,
+        latitude: 39.74 * RAD,
+        height: 1900,
+      },
+    },
+    scene: { globe: { show: globeShown, getHeight: () => globeHeight } },
+  };
+}
+
+test('a shown globe answers the ground under the camera', () => {
+  assert.equal(
+    cameraHeightAboveGround(viewer({ globeShown: true, globeHeight: 1600 })),
+    300,
+  );
+});
+
+test('a hidden globe (Google 3D) falls back to the bare-earth height', () => {
+  const calls = [];
+  const groundAt = (lon, lat) => {
+    calls.push([+lon.toFixed(2), +lat.toFixed(2)]);
+    return 1600;
+  };
+  // A hidden globe's getHeight is ignored even when it returns a number.
+  const hidden = viewer({ globeShown: false, globeHeight: 0 });
+  assert.equal(cameraHeightAboveGround(hidden, { groundAt }), 300);
+  assert.deepEqual(calls, [[-104.99, 39.74]]);
+});
+
+test('with no ground sample the ellipsoidal height is used', () => {
+  const hidden = viewer({ globeShown: false, globeHeight: 0 });
+  assert.equal(cameraHeightAboveGround(hidden), 1900);
+  assert.equal(cameraHeightAboveGround(hidden, { groundAt: () => null }), 1900);
+  assert.equal(cameraHeightAboveGround({}), null);
+});