Plan KML and KMZ drawing in one pure function, checked against Cesium

src/data/geoImportPlan.js decides what an imported file draws and with
what: raised or clamped geometry, rings and holes, rotation near the
poles and across 360 degrees, absolute and relative altitudes, draw
order, canvas budgets and the vertex and ring limits, with no engine and
no DOM. drawImportedFile draws that plan through the globe contract and
keeps pin placement, yielding and cancellation. Every limit of the import
lives in src/data/geoImportLimits.js with what it protects.

scripts/fixtures/geo-import holds 13 files covering those cases, and
reference.json what Cesium's own KML and GeoJSON data sources make of
them; scripts/qa-geo-import-reference.mjs records it and compares the
plan with it. Property tests on seeded random polygons check area,
bounds, ring closure and winding. Writing the plan fixed three cases:
overlays below the ellipsoid kept a negative height, raised plain-colour
overlays now draw, and the vertex limit no longer depends on whether a
ring repeats its first point.

docs/GLOBE-PRIMITIVES.md

@@ -350,12 +350,13 @@ Raised polygons (KML absolute or relative) draw their fills as meshes and
 their outlines as lines at the vertices' heights. A ground overlay's colour
 tints its image and its alpha fades it; a rotated overlay's image is turned
 on a canvas over the box around it, as Cesium turns its rectangle in degrees,
-and an absolute overlay is raised to its altitude (Cesium raises only
-absolute ones). The shared display has known limits against Cesium: wall
-fills and extruded prisms are omitted (their top geometry remains), and
-`gx:LatLonQuad`, a rotated overlay whose box passes a pole and a raised
-plain-colour overlay are omitted. These are counted as undrawn. Ground edges
-use great circles rather than rhumb lines.
+and an absolute image or plain-colour overlay is a mesh at its altitude,
+including negative heights (Cesium raises only absolute ones).
+The shared display has known limits against Cesium: wall fills and extruded
+prisms are omitted (their top geometry remains), and
+`gx:LatLonQuad` and a rotated overlay whose box passes a pole are omitted.
+These are counted as undrawn. Ground edges use great circles rather than
+rhumb lines.
 
 ## Input ownership