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.

changelog.d/1519-range-ring-sonar-pulses.md

@@ -1,6 +1,8 @@
 - The Global Context range ring pulses like a sonar: three dim rings with a
   soft inward glow grow from the subject to 250 km, and the ring flashes as
   each one arrives. Flights, military aircraft and AIS vessels a pulse crosses
-  get a brief echo around their brackets. While a subject is shown, a parked
-  Contacts view repaints about 12 times a second. Under reduced motion there
-  are no pulses and the ring stays on screen (manjunath22466, #1519).
+  get a brief echo around their brackets. The pulses run for about 9 s after
+  a selection or camera move, dimming the ring between flashes, then rest
+  with the ring steady on screen, so a parked view stops repainting. Under
+  reduced motion there are no pulses and the ring stays on screen
+  (manjunath22466, #1519).