feat(awareness): add calm sonar pulses that flash the range ring and echo contacts

Pulses: three dim rings grow from the Global Context subject to the
250 km range ring at constant speed, one every 3 s, each taking 9 s.
Each fades in over its first 8% of travel, then fades as
(1 - travel)^1.5 to about a third of its 60% peak, so it arrives at the
ring dim but visible. They are 3 px in the ring's colours, as polylines
with CallbackProperty positions and colours that share the ring's
centre object, so they follow a moving subject.

Ring: while pulses run, the 250 km ring rests unseen and flashes to full
strength as each pulse reaches it, fading over 1.8 s. Without pulses
(reduced motion, or a scene with no primitives or preRender hook) it
stays on screen as before.

Gradient: behind each pulse a radial band in the same blue fades inward
over 35% of the radius. One flat, translucent, unpickable 250 km disc
draws it with a small Fabric material. A preRender listener writes the
pulse radii and opacities into two vec4 uniforms each frame. The disc
(0.25 degree granularity, ~3.5 ms to build) is rebuilt only after the
subject moves 2 km.

Echoes: as a pulse front crosses a flight, military aircraft or AIS
vessel, the detection overlay draws a second bracket in the pulse blue
around that contact's own bracket, spreading outward as it fades over
1.4 s. Awareness publishes the field (centre, radius, pulse timing,
echo styling) through the new src/awarenessEcho.js. The overlay reads
it, so no layer's icon or colour is touched. Mapped installations have
no detection bracket, so they do not echo.

Rendering cost: pulses never hold continuous rendering. They ask for a
frame every 80 ms, the Cyber sonar's parked cadence, so a parked
Contacts view repaints at ~12.5 fps while a subject is shown. This
changes the "parked Contacts stays quiet" behaviour on purpose.
clearVisual stops the timer and removes the disc, the listener and the
echo field.

awarenessRangeRingPositions can now reuse a result array, and passes the
WGS84 ellipsoid explicitly so a reused Cartesian never lands in the
ellipsoid argument. Tuning lives in AWARENESS_RANGE_PULSE,
AWARENESS_RANGE_ECHO and AWARENESS_RANGE_RING_STYLE. src/awarenessEcho.js
is registered in the awareness-layer, application-components and
application-layer-construction packages.

Tests cover:
- the pulse curve and calm rate;
- the ring flash once per arrival, and the static ring without pulses;
- the 80 ms frame cadence and its stop;
- the partial-scene fallback;
- the gradient disc: unpickable, uniform values, rebuild and cleanup;
- per-frame evaluation, and the echo field following the subject;
- awarenessEcho strength, rim wrap, layer filter and altitude handling;
- the detection renderer's echo-bracket band and outward spread.

docs/CURRENT-STATE.md

@@ -4957,7 +4957,7 @@ silently demoting every later lookup for the session.
 - Enabled Data Layer controls report normalized feed health on the button (`LOADING`, `DEGRADED`, `STALE`, `FALLBACK`, or `UNAVAILABLE`) while the metadata line retains the source and reason. A partial CelesTrak group failure keeps the usable catalog and reports `DEGRADED`; a total outage keeps last-good catalog data visible but reports `UNAVAILABLE`.
 - On activation it focuses the nearest currently observed aircraft across the civilian and military feeds, with military winning an exact distance tie; if none are available, it focuses an observed AIS vessel. The aircraft search is deliberately uncapped and one refresh-tick retry handles initially empty feeds. This is an attention-priority navigation shortcut, not a high-risk, affiliation, or threat classification.
 - A selected aircraft, AIS vessel, or mapped installation gets a 250 km **context window** with nearby cohort counts, nearest examples, source labels, and stale/unavailable reasons. It emits `NEARBY` or `UNKNOWN`; no detection, engagement, affiliation, or sensor-activity conclusion is calculated.
-- The window's edge is drawn on the globe as a 250 km range ring: a 4 px polyline with a 2 px Context-blue core inside a 1 px dark halo on each side, 2.5 km above the ellipsoid (`AWARENESS_RANGE_RING_STYLE` in `src/layers/awareness/policy.js`). The halo keeps it legible over bright desert and snow, dark ocean and forest, and under the FLIR, NVG and CRT styles, where the earlier 1 px ellipse outline disappeared. It is a polyline because WebGL draws ellipse outlines at 1 px whatever width is asked for. The ring follows a moving subject once it has moved 250 m.
+- The window's edge is drawn on the globe as a 250 km range ring: a 4 px polyline with a 2 px Context-blue core inside a 1 px dark halo on each side, 2.5 km above the ellipsoid (`AWARENESS_RANGE_RING_STYLE` in `src/layers/awareness/policy.js`). The halo keeps it legible over bright desert and snow, dark ocean and forest, and under the FLIR, NVG and CRT styles, where the earlier 1 px ellipse outline disappeared. It is a polyline because WebGL draws ellipse outlines at 1 px whatever width is asked for. Three dim sonar pulses (3 px, same colours, at most 60% opacity) grow slowly from the subject at constant speed, one every 3 s and each taking 9 s, and arrive at the ring at about a third of that. Behind each pulse a radial gradient in the same blue fades inward over 35% of the radius, drawn by one unpickable 250 km disc whose shader reads the pulse radii and opacities each frame; the disc itself is rebuilt only after the subject moves 2 km. While pulses run, the ring is not shown on its own: it flashes to full strength as each pulse reaches it and fades over 1.8 s. As a pulse front crosses a flight, military aircraft or AIS vessel, the detection overlay draws a second bracket in the pulse blue around that contact's own bracket, which spreads outward as it fades over 1.4 s (`AWARENESS_RANGE_ECHO`, read through `src/awarenessEcho.js`; no layer's icon is restyled, and mapped installations have no detection bracket). Pulses never hold continuous rendering: they ask for a frame every 80 ms, the Cyber sonar's parked cadence, so a parked Contacts view repaints at about 12.5 fps while a subject is shown, and at full rate only when something else already renders continuously. Under `prefers-reduced-motion`, or in a scene without primitives or a preRender hook, there are no pulses or echoes and the ring stays on screen. The ring follows a moving subject once it has moved 250 m.
 - For a selected live aircraft or vessel, the context window refreshes from the existing tracker/feed position every 750 ms, so nearest distances and cohort counts follow the subject without introducing a duplicate poll loop.
 - Aircraft cohort membership uses every locally loaded, selectable contact inside the 250 km window, including a plane hidden only by horizon culling or because its 3D model owns the visual. Counts and navigation therefore do not change with the current camera angle or billboard/model handoff.
 - Nearby examples in the context panel are focus controls: they use their owning layer's existing selection/tracking path, then frame that contact. Static-installation distances use ellipsoidal surface distance so the count matches the ground-projected context disk.