fix(import): address review on metadata, bounds, navigation, clock and GPX

- Imported metadata stays inert: descriptions, native labels, properties and
  KML extended data are dropped from every entity; names are kept as short
  plain text. GeoJSON loads with a describe that builds no HTML, and
  simplestyle (including marker-symbol) is dropped, so no icon asset is
  fetched for a file and GeoJSON draws in its row's color.
- Bound geometry before loading: features and vertices are counted in the
  parsed GeoJSON, the KML document and while reading GPX, and a file over
  20,000 features or 250,000 vertices is refused before Cesium builds it.
- Imports run one batch at a time, so concurrent picks or drops cannot pass
  the 12-file cap.
- Fly-to framing walks long tracks by index instead of spreading them into a
  call.
- Fly-to is an immediate navigation through the application shell; the fly
  after an import is a deferred navigation stamped when the batch starts and
  re-asserted just before flying.
- Dated imports never change the shared clock: imported sources expose no
  clock, entities are available for all time, and a KML gx:Track is drawn as
  its line.
- GPX is read into GeoJSON with one line per track segment, without times.
- KML/KMZ rows show a hatched swatch (they keep their own styles); keyboard
  focus is kept on the same control after hide/show and moves to the next
  row after remove.
- Unit regressions for each, and the rendered QA now imports hostile
  metadata, dated KML/GPX and a two-segment track, and fails on any request
  for a file's contents or icon assets, a clock change, or surviving
  metadata.

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

src/ui/flyToDataSource.test.mjs

@@ -57,3 +57,20 @@ test('the camera frames the footprint at the surface, never a buried center', ()
   );
   assert.equal(calls.at(-1), 'viewer.flyTo');
 });
+
+test('a very long track is framed without spreading it into a call', () => {
+  // 400k vertices: `push(...line)` throws RangeError (too many arguments)
+  // well below this; the walk keeps a bounded sample and both ends.
+  const n = 400_000;
+  const line = new Array(n);
+  for (let i = 0; i < n; i++)
+    line[i] = Cesium.Cartesian3.fromDegrees(-120 + (i / n) * 2, 40);
+  const ds = new Cesium.CustomDataSource('long');
+  ds.entities.add({ polyline: { positions: line } });
+  ds.entities.add({ position: Cesium.Cartesian3.fromDegrees(-110, 41) });
+  const points = dataSourcePoints(ds);
+  assert.ok(points.length <= 5002, `${points.length} points kept`);
+  const lons = points.map(([lon]) => lon);
+  assert.ok(Math.min(...lons) < -119.99 && Math.max(...lons) > -110.01);
+  assert.ok(lons.some((lon) => Math.abs(lon - -118.000005) < 0.01));
+});