Draw civil flights from an icon set moved on the GPU

Every flight is now a row in the layer's icon set. Its motion segment
follows the same regime `_deadReckon` picks (interpolate between fixes,
warm up backward from the oldest, coast forward from the newest), and
one shared `_motionRegime` makes that choice for both. The shader moves
every untracked contact between polls, so the 12 Hz fleet tick no
longer touches each billboard. It now only re-plans expired rows,
floors grounded contacts, advances focus while needed, and runs the 3D
model regime.

Grounded contacts the floor lifts are pinned to a hold at the floored
position. Their nose glides on the GPU. Contacts within 50 km re-floor
every tick, and farther ones take turns about once a second. Low
contacts are judged for the horizon at no lower than 12 m above the
ellipsoid, as before. Below hover speed a contact's nose holds. A row
whose fleet model is drawn keeps its focus updated, because the model
reads it. Untracking re-plans and re-floors the icon from the tracked
course.

On the same views with about 6,700 OpenSky flights, frame gaps at p95
drop from 28-40 ms to 17 ms, and the fleet tick from 16-37 ms to about
2 ms at most.

scripts/package-boundaries.json

@@ -1315,6 +1315,12 @@
       "src/layers/flights/policy.js",
       "src/layers/flights/queries.js",
       "src/layers/flights/rendering.js",
+      "src/layers/flights/icons.js",
+      "src/data/iconSetPrimitive.js",
+      "src/data/iconSet.js",
+      "src/data/iconSegment.js",
+      "src/data/iconAtlas.js",
+      "src/data/aircraftRecession.js",
       "src/data/modelMirror.js",
       "src/data/billboardMirror.js",
       "src/layers/aircraft/visualState.js",
@@ -2249,6 +2255,7 @@
       "./standalone/catalog"
     ],
     "modules": [
+      "src/layers/flights/icons.js",
       "src/sources/adsbFields.js",
       "src/data/headingDegrees.js",
       "src/data/distanceFormat.js",
@@ -3248,6 +3255,11 @@
   "application-layer-construction": {
     "exports": ["./application/layers"],
     "modules": [
+      "src/layers/flights/icons.js",
+      "src/data/iconSetPrimitive.js",
+      "src/data/iconSet.js",
+      "src/data/iconSegment.js",
+      "src/data/iconAtlas.js",
       "src/sources/adsbFields.js",
       "src/data/headingDegrees.js",
       "src/data/distanceFormat.js",