refactor(localAdsb): Cesium rendering behind a renderer interface

Task 12a. The Local ADS-B logic (index.js, models.js) no longer imports
Cesium. src/layers/localAdsb/render/cesium.js holds what it built, one
for one: the CustomDataSource of marker entities (billboard with
per-frame position/rotation/visibility CallbackProperties, the 2,000 km
DistanceDisplayCondition, the 978 MHz UAT ring as a PointGraphics), the
model PrimitiveCollection (models load, pose and leave through the shared
aircraft renderer's model part, adopting that collection), the selected
aircraft's trail (data/trailRenderer, as before) and live head segment,
and the camera reads. Registered for 'local-adsb' in the renderer
registry, created at init(viewer, {engine}).

- Clicks go through the engine's selection dispatcher (drill 8) instead of
  the layer's ScreenSpaceEventHandler, with the layer's own rule kept as is
  — a new `lookUnder` owner kind: its marker on top, or under picks no
  layer owns and under trail lines, is selected (and re-selected);
  another layer's contact on top, or empty map, releases only its own
  selection; a trail line alone does nothing; no gesture rule. To the
  other owners it is another layer, as its pick-owner registration made
  it before. (The dispatcher's `drillThrough` would have taken the marker
  from under another layer's contact, which the old handler never did.)
- models.js reads the camera through the renderer's view (frustum and
  horizon tests, ground snap owner) and draws through renderer.models
  (loadFleet/add/remove/destroy/setPose: the same MIX-tinted glTF options,
  the same HPR frame with the Flights nose offset). The shared aircraft
  renderer gains a loadModel seam (default Cesium.Model.fromGltfAsync).
- Cesium math → src/geo; the model tint is an Rgba equal to the old
  Cesium.Color; check-import-directions: src/layers/localAdsb/ joins the
  rendered layers.

Tests moved with the code, same meaning:
- index.test: the services fixture creates the layer's Cesium renderer and
  the selection dispatcher; the click harness scripts the picks on a fake
  engine registered for the fake viewer (was a fake ScreenSpaceEventHandler)
  and the app's pick owners (trails, a Flights contact) are registered in
  the pick registry (was an injected picking service).
- cockpitModels.test: the GLB loads are the aircraft renderer's loadModel
  calls (Cesium.Model.fromGltfAsync by default), each asynchronous:false.
- trackingClickGesture.test: the dispatcher's empty click goes to the
  plain owners (filter(plain)).
- renderers.test: local-adsb has an extracted Cesium renderer.
New: the dispatcher's look-under rule beside a plain owner (7 click cases).

W1 replay (flights, military, localAdsb) vs a fresh 7c7422e2 run: counts,
known objects, screen points, tracking poses, requests and every shot's
sha256 identical.

scripts/package-boundaries.json

@@ -2600,7 +2600,8 @@
       "src/layers/aircraft/render/navara.js",
       "src/layers/flights/render/navara.js",
       "src/layers/military/render/navara.js",
-      "src/layers/aircraft/qaDrawn.js"
+      "src/layers/aircraft/qaDrawn.js",
+      "src/layers/localAdsb/render/cesium.js"
     ],
     "external": [
       "hls.js",
@@ -3177,7 +3178,8 @@
       "src/layers/shared/color.js",
       "src/layers/flights/render/cesium.js",
       "src/layers/military/render/cesium.js",
-      "src/layers/aircraft/qaDrawn.js"
+      "src/layers/aircraft/qaDrawn.js",
+      "src/layers/localAdsb/render/cesium.js"
     ],
     "external": [
       "hls.js",