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/radio.mjs

@@ -0,0 +1,109 @@
+// Shared 750-station directory for legacy and both-engine radio QA.
+const tags = [
+  'news',
+  'talk',
+  'weather,emergency',
+  'public safety,scanner',
+  'aviation,atc',
+  'marine,maritime',
+  'traffic,transit',
+  'music,jazz',
+  'music,rock',
+  'community',
+];
+export const stations = Array.from({ length: 750 }, (_, index) => {
+  const row = Math.floor(index / 30);
+  const column = index % 30;
+  return {
+    id: `00000000-0000-4000-8000-${index.toString(16).padStart(12, '0')}`,
+    name:
+      index === 360
+        ? '100.3 The River - WQRV - Meridianville/Huntsville, AL'
+        : index === 390
+          ? 'La Zeta (Hermosillo) - 93.9 FM - XHHY - Uniradio - Hermosillo, Sonora'
+          : `QA Radio ${String(index + 1).padStart(3, '0')}`,
+    lat: -72 + row * 6,
+    lon: -174 + column * 12,
+    streamUrl: `https://audio.example.test/${index}.mp3`,
+    homepage: `https://station.example.test/${index}`,
+    tags: tags[index % tags.length].split(','),
+    languages: index === 360 ? ['Spanish'] : ['English'],
+    state: `Region ${row + 1}`,
+    country: 'United States',
+    countryCode: 'US',
+    metadataTrust: 'untrusted-community',
+    codec: index % 2 ? 'AAC' : 'MP3',
+    bitrate: 128,
+  };
+});
+
+export async function installRadioFixture(page) {
+  await page.evaluateOnNewDocument((stations) => {
+    localStorage.clear();
+    localStorage.setItem('gev:first-run-mission:v1', 'suppressed');
+    window.__qaRadio = {
+      stations,
+      generation: 1,
+      plays: [],
+      delay: 0,
+      response: 'normal',
+      pending: null,
+    };
+    HTMLMediaElement.prototype.play = function () {
+      window.qaPlayer = this;
+      window.__qaRadio.plays.push(this.src);
+      if (window.__qaRadio.delayPlay) {
+        window.__qaRadio.delayPlay = false;
+        return new Promise((resolve) => {
+          window.__qaRadio.releasePlay = () => {
+            this.dispatchEvent(new Event('playing'));
+            resolve();
+          };
+        });
+      }
+      queueMicrotask(() => this.dispatchEvent(new Event('playing')));
+      return Promise.resolve();
+    };
+    const fetch = window.fetch.bind(window);
+    window.fetch = async (input, init) => {
+      const address = String(
+        typeof input === 'string' || input instanceof URL ? input : input.url,
+      );
+      if (address.includes('/api/radio/stations')) {
+        const qa = window.__qaRadio;
+        qa.reads = (qa.reads || 0) + 1;
+        const response = {
+          stations: qa.response === 'empty' ? [] : qa.stations,
+          updatedAt: new Date().toISOString(),
+          stale: false,
+          degraded: false,
+          acceptedGeneration: qa.generation,
+          catalogInstance: 'fixture-radio-fixture',
+        };
+        const mode = qa.response;
+        const delay = qa.delay;
+        qa.delay = 0;
+        if (delay)
+          await new Promise((resolve) => {
+            qa.pending = resolve;
+          });
+        init?.signal?.throwIfAborted();
+        return new Response(
+          mode === 'failure' ? '{}' : JSON.stringify(response),
+          {
+            status: mode === 'failure' ? 503 : 200,
+            headers: { 'Content-Type': 'application/json' },
+          },
+        );
+      }
+      if (address.includes('/api/radio/click/'))
+        return new Response(null, { status: 204 });
+      if (address.includes('/api/flights'))
+        return new Response('{"states":[]}');
+      if (address.includes('/api/military')) return new Response('{"ac":[]}');
+      if (address.includes('/api/vessels'))
+        return new Response('{"connected":false,"vessels":[]}');
+      return fetch(input, init);
+    };
+  }, stations);
+}