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]>

CHANGELOG.md

@@ -30,11 +30,15 @@
   under NLOD 2.0.
 
 - Import your own GeoJSON, KML, KMZ and GPX files (DISPLAY ▸ Import, or drop
-  them onto the globe). Each file is drawn on the ground in its own color with
-  a row to show, hide, fly to or remove it. Files stay in the browser for the
-  session, and KML/KMZ network links, remote icons, remote styles and balloon
-  HTML are left out so an imported file cannot make the page fetch anything.
-  The import half of #890.
+  them onto the globe). GeoJSON and GPX files are drawn on the ground in the
+  color shown on their row; KML and KMZ keep the styles written in them. Each
+  file gets a row to show, hide, fly to or remove it. Files stay in the
+  browser for the session. An import cannot make the page fetch anything (KML
+  network links, remote icons and styles are left out), keeps only plain-text
+  names from the file (no descriptions, balloons or native labels), never
+  moves the app's clock (dated tracks draw for all time), and keeps GPX track
+  segments apart. Size limits are checked before anything is built. The import
+  half of #890.
 
 ## [0.2.1] — 2026-10-02 — God's Eye View through Your Agent (with security fixes and other features)