feat(globe): surface height quality

engine.surface.sampleHeightDetailed(place, { exclude, lod }) answers
{ height, source: 'tiles' | 'terrain', tileSizeM? } (src/globe/surfaceDetail.js).
On Navara tileSizeM is the extent of the tile that answered and
lod 'finest' takes the finest loaded tile, drawn or not; Cesium answers
tiles without a size, else the globe's terrain. acceptedSurfaceHeight()
turns an answer into a height or a miss: tiles larger than
MAX_FLOOR_TILE_SIZE_M (4 km) are too coarse, terrain is not the mesh.

The mesh floor sampler and the ground snap are engine-only now (a viewer
or scene reaches its engine through engineFromViewer, which also registers
the scene) and treat a coarse answer as a miss, as they treat undefined.
Measured on Navara at Austin: while the tiles stream, a 27.9 km tile reads
143.2 m where the ground is 122.5 m (a 1.8 km tile).

`exclude` takes the engine's own mover sets (MoverSet.id): Cesium hides a
set's primitive for the synchronous sample (Cesium matches excluded objects
per billboard, not per collection); Navara's ray only meets tiles.

"sampleHeight undefined in the app on Navara" did not reproduce: the
startup Austin sample is 121.9 m (tile 889 m) on Navara and 122.4 m on
Cesium; one ModelMesh class is patched.

S2 QA (scripts/qa-surface-heights.mjs, 20 places at JFK, SFO, AUS, roofs
and streets): Navara within 2 m of Cesium at 19/20 from 800 m and 18/20
from 15 km with lod 'finest' (gates 18 and 15); offsets per region
-0.21 / +0.4 / +0.1 m; the Empire State roof differs by 39 m (spire
geometry). Navara tile sizes at 800 m: 112-314 m.

scripts/package-boundaries.json

@@ -2563,7 +2563,8 @@
       "src/globe/navara/movers/moverMesh.js",
       "src/globe/navara/movers/pack.js",
       "src/globe/navara/movers/modelMover.js",
-      "src/globe/navara/movers/index.js"
+      "src/globe/navara/movers/index.js",
+      "src/globe/surfaceDetail.js"
     ],
     "external": [
       "hls.js",
@@ -3214,7 +3215,8 @@
       "src/geo/scaleToGeodeticSurface.js",
       "src/geo/check.js",
       "src/geo/debug.js",
-      "src/geo/developerError.js"
+      "src/geo/developerError.js",
+      "src/globe/surfaceDetail.js"
     ],
     "external": [
       "cesium",
@@ -3694,7 +3696,8 @@
       "src/geo/check.js",
       "src/geo/debug.js",
       "src/geo/developerError.js",
-      "src/time/clock.js"
+      "src/time/clock.js",
+      "src/globe/surfaceDetail.js"
     ],
     "external": ["cesium", "egm96-universal", "pbf"]
   },