Test layers on one engine and share selection and shader helpers

Layer display tests no longer re-check Cesium primitives in every layer:
they run on the fake engine, and one Cesium translation check per ground
kind lives in the Cesium engine's ground tests. Their harnesses are shared,
and the fake-engine, Cesium-engine and flights tests that repeated the
contract suite are gone, 340 tests in all.

The press-travel measurement is shared by the selection dispatcher and
CCTV, which loses its ScreenSpaceEventHandler shim and world-click module.
ALPR, installations and bikeshare share one selection keeper and selected
marker write. Layers with their own click rules keep their handlers.

Navara's pulse is a class like the ground pass, the ground and imagery
passes share the surface uniforms, and the colour, log-depth and occlusion
GLSL lives in one chunk module, each caller keeping its depth bias. The
ground suite runs inside the contract suite (--only=ground:), and fixture
and script names say what they test.

Behaviour is unchanged on both engines.

docs/CURRENT-STATE.md

@@ -208,7 +208,7 @@ one application, and only the globe-bound parts move to the next engine.
     segments (`corridors.js`): 10,000 corridors draw in about 12 ms still
     and 14 ms moving, where Cesium takes 23 ms (the chunks before took 151
     and 196 ms).
-  - `scripts/qa-ground-suite.mjs` checks ground pixels and corridor looks
+  - `scripts/qa-contract-suite.mjs --only=ground:` checks ground pixels and corridor looks
     on both engines.
 - **Ground and input parity.** Space Missions draws its 500 m launch-pad
   zone with the radial ground material: faint fill, bright soft rim and
@@ -249,7 +249,7 @@ one application, and only the globe-bound parts move to the next engine.
   - Sea Marks and Ski Pistes use `engine.imagery` on engines without
     `maps.addOverlay`; Navara retains its native raster path for tile detail.
     Imported KML/KMZ ground images use imagery on both engines.
-  - `scripts/qa-ground-suite.mjs --only=imagery:` checks imagery pixels
+  - `scripts/qa-contract-suite.mjs --only=imagery:` checks imagery pixels
     on both engines. Navara mipmaps the heatmap at orbit scale.
 - **Engine coupling.** `node scripts/report-engine-coupling.mjs` counts the
   engine-specific code outside the engines: renderer lines per engine, Cesium