fix(awareness): bound the range ring pulses so a parked view goes quiet

Review follow-up for the sonar pulses.

Bounded repaint: the pulses used to ask for a frame every 80 ms from a
setInterval for as long as a subject was shown, so a parked view
repainted at 12.5 fps indefinitely. They now run for 9 s (three ring
flashes) after a selection or a camera move, fading in and out over
1.2 s, then rest: the ring stands on screen at full strength, the pulse
lines and gradient disc are hidden, echoes stop, and nothing asks for
frames. A moving subject does not wake them, since a flying subject
moves on every refresh. The lifecycle's existing camera pose signature
wakes them.

No beat with the Cyber sonar: the setInterval is replaced by a
postRender-armed setTimeout on CYBER_SONAR_RENDER_INTERVAL_MS, as in
cyberSonarScene. Every drawn frame, whoever asked for it, re-arms the
request 80 ms later, so requests never land inside the detection
lane's 80 ms gate.

Reduced motion mid-session: a change listener on the media query
rebuilds the visual, and the same-subject refresh path rebuilds when
the preference no longer matches. The listener is removed in
clearVisual.

Readable edge: restOpacity goes from 0 to 0.4, so the 250 km ring stays
visible between flashes, in screenshots and for low-vision viewers.

The echo field takes an optional level so echoes rest with the pulses.
CURRENT-STATE and the changelog fragment describe the bounded run and
the dimmed ring.

Tests: render requests stop after the bound and stay stopped for a
minute; a camera move seen by the lifecycle wakes them for another
bounded run; a foreign frame postpones the next request to 80 ms after
it; reduced motion flipped by event and by a later refresh; the ring
never drops below restOpacity; echoes scale with the level; the level
fades in, holds, fades out and keeps its value when woken.

src/awarenessEcho.test.mjs

@@ -82,3 +82,28 @@ test('awarenessEchoAt reads the published field, by layer, at ground level', (t)
   assert.equal(getAwarenessEchoField(), null);
   assert.equal(awarenessEchoAt('flights', contact, t0), 0);
 });
+
+test('echoes scale with the field level and rest with the pulses', (t) => {
+  t.after(clearAwarenessEchoField);
+  const center = Cesium.Cartesian3.fromDegrees(3, 27, 0);
+  // ~100 km east of the subject, on the ground.
+  const contact = Cesium.Cartesian3.fromDegrees(4.008, 27, 0);
+  let level = 1;
+  setAwarenessEchoField({
+    center,
+    radiusM: R,
+    pulse,
+    echo,
+    level: () => level,
+  });
+  const d = Cesium.Cartesian3.distance(center, contact);
+  const t0 = arrival(d);
+  const full = awarenessEchoAt('flights', contact, t0);
+  assert.ok(full > 0.99);
+  level = 0.5;
+  assert.ok(
+    Math.abs(awarenessEchoAt('flights', contact, t0) - full / 2) < 1e-9,
+  );
+  level = 0;
+  assert.equal(awarenessEchoAt('flights', contact, t0), 0);
+});