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.

scripts/fixtures/layers/alpr.mjs

@@ -13,7 +13,7 @@ export const cameras = [
 ].map((position, i) => ({
   ...position,
   osmId: 9000000 + i,
-  operator: i % 3 ? 'W2 fixture' : 'Cámara pública',
+  operator: i % 3 ? 'Deterministic fixture' : 'Cámara pública',
   brand: 'Fixture camera',
   cameraType: 'fixed',
   direction: i % 5 ? String((i * 37) % 360) : '',

scripts/fixtures/layers/cctv.mjs

@@ -2,8 +2,8 @@ import sharp from 'sharp';
 
 // Transport fixtures are parsed by the real CCTV catalog and media owners.
 export const cameras = Array.from({ length: 25 }, (_, i) => ({
-  id: `w2-cctv-${String(i).padStart(3, '0')}`,
-  name: i === 12 ? 'Cámara pública — Congress' : `W2 camera ${i}`,
+  id: `fixture-cctv-${String(i).padStart(3, '0')}`,
+  name: i === 12 ? 'Cámara pública — Congress' : `Fixture camera ${i}`,
   cityId: 'austin',
   city: 'Austin',
   lat: 30.2672 + (Math.floor(i / 5) - 2) * 0.0018,
@@ -17,7 +17,7 @@ export const cameras = Array.from({ length: 25 }, (_, i) => ({
   headingConfidence: i % 3 ? 'medium' : 'low',
   sourceKind: 'configured',
   feedType: 'image',
-  provider: 'W2 deterministic fixture',
+  provider: 'Deterministic fixture',
   url: 'https://cctv-fixture.invalid/frame.png',
 }));
 
@@ -51,8 +51,8 @@ export async function installCctvFixture(page, { video } = {}) {
   if (video)
     catalog.push({
       ...cameras[0],
-      id: 'w2-cctv-video',
-      name: 'W2 moving video',
+      id: 'fixture-cctv-video',
+      name: 'Fixture moving video',
       lat: 30.2718,
       lon: -97.744,
       feedType: 'video',
@@ -116,7 +116,7 @@ export async function installCctvFixture(page, { video } = {}) {
           id,
           status: 'online',
           sourceKind: feedType,
-          label: 'W2 deterministic fixture',
+          label: 'Deterministic fixture',
           updatedAt: Date.now(),
         })),
       });
@@ -126,7 +126,7 @@ export async function installCctvFixture(page, { video } = {}) {
       const id = decodeURIComponent(media[2]);
       if (
         !ids.has(id) ||
-        (media[1] === 'media' && (id !== 'w2-cctv-video' || !video))
+        (media[1] === 'media' && (id !== 'fixture-cctv-video' || !video))
       ) {
         return request.respond({ status: 404, body: 'Unknown fixture camera' });
       }

scripts/fixtures/layers/combined.mjs

@@ -4,8 +4,8 @@ const grid = (i, cols, spacing) => ({
   lon: ORIGIN.lon + ((i % cols) - cols / 2) * spacing,
 });
 const bikes = Array.from({ length: 200 }, (_, i) => ({
-  station_id: `w2-bike-${i}`,
-  name: `W2 station ${i}`,
+  station_id: `fixture-bike-${i}`,
+  name: `Fixture station ${i}`,
   capacity: 20,
   ...grid(i, 15, 0.0015),
 }));

scripts/fixtures/layers/radio.mjs

@@ -78,7 +78,7 @@ export async function installRadioFixture(page) {
           stale: false,
           degraded: false,
           acceptedGeneration: qa.generation,
-          catalogInstance: 'w2-radio-fixture',
+          catalogInstance: 'fixture-radio-fixture',
         };
         const mode = qa.response;
         const delay = qa.delay;

scripts/fixtures/layers/transit.mjs

@@ -6,7 +6,7 @@ export function transitSnapshot(step = 8) {
     fetchedAt,
     vehicles: [
       ...Array.from({ length: 12 }, (_, i) => ({
-        id: `w2-${i}`,
+        id: `fixture-${i}`,
         routeId: routes[i % 6],
         tripId: `trip-${i}`,
         lat: