fix(awareness): make the 250 km range ring readable on any ground

The Global Context range ring was a Cesium ellipse outline at 1 px in
rgba(98,181,255,0.72). WebGL ignores larger ellipse outline widths, so it
could not be thickened, and it vanished over desert and snow and under the
FLIR, NVG and CRT styles.

Draw it as a polyline instead: a 4 px line with a 2 px Context-blue core
inside a 1 px dark halo on each side (PolylineOutlineMaterialProperty).
The halo gives luminance contrast on light and dark ground, which the
monochrome styles keep. The ring sits at the same 2.5 km height and
follows the subject on the same 250 m threshold. Positions come from a
new awarenessRangeRingPositions helper that stays within 50 m of 250 km.

Style values live in AWARENESS_RANGE_RING_STYLE (awareness/policy.js).
Adds rangeRing.test.mjs (geometry at equator, Sahara, Greenland and the
antimeridian; contrast; entity shape; follow threshold) and a
CURRENT-STATE note.

scripts/format-scope.json

@@ -1177,6 +1177,7 @@
   "src/overlays/worldOverlayActionsView.test.mjs",
   "src/ui/stores/awarenessDirection.js",
   "src/layers/awareness/directionOverlay.test.mjs",
+  "src/layers/awareness/rangeRing.test.mjs",
   "src/hudReadouts.js",
   "src/ui/stores/hud.js",
   "src/ui/views/intelHudView.test.mjs",