Let a host application place live contacts

createApplicationCatalog takes an optional placement provider. Its
layer(kind) hands Flights, Military Flights, AIS Vessels, Transit and Rail
a place(id, wallMs), and optionally observe(id, fix) and forget(id). While
live, each layer tells it every fix it accepts and draws a contact where it
places it: position, height (the layer's own when none is given), course
and speed. A null answer, a provider that throws, a kind it leaves out, or
no provider at all keeps the layer's own motion unchanged, and following
the world clock the layers never ask it. A transit vehicle or train it
holds still lets the render loop idle and is asked again each second;
vessels ask for frames only while it places one, and stop when the layer
turns off.

Tests show the layers draw and reconcile exactly as before without a
provider and with one that places nothing, draw where a provider places
them, and idle while it holds them still.

scripts/format-scope.json

@@ -1457,5 +1457,7 @@
   "src/ui/styles/rail-edge.css",
   "src/ui/styles/rail-split.css",
   "src/ui/styles/left-tools.css",
-  "src/ui/styles/panel-edge.css"
+  "src/ui/styles/panel-edge.css",
+  "src/data/placementProvider.test.mjs",
+  "src/layers/vessels/placement.test.mjs"
 ]