Fly the remaining flights through the camera port, on any viewer

The embed view, the celestial-ring focus, the ground-guard lift, the
Bhote Koshi approach and orbit, launch selection and replay flights, and
the cockpit's view and takeover now drive the renderer's camera port.
The contract gains a sineInOut easing, pinned by a conformance trace.

A viewer with no renderer bound, such as one a consumer of a public
export brings, now gets a camera port too, as it already got an input
port: cameraOf builds one over the viewer's own Cesium camera and keeps
it for the viewer's life, until a renderer is bound. The Cesium adapter
provides the factory as it loads; code that reaches Cesium takes cameraOf
from the adapter so the factory comes with it, and findCamera answers
null where a missing camera is not an error (HUD, share link, world
focus, Recent Imagery's ZOOM IN). A test walks every package export and
fails one that can reach the bridge without loading the factory.

A destroyed viewer gets no camera and lets go of a built one, and the
application renderer stays bound until its viewer is destroyed.

src/app/embed.js

@@ -13,6 +13,7 @@
 
 import * as Cesium from 'cesium';
 import { announceNavigationAuthority } from '../navigationPolicy.js';
+import { cameraOf } from '../render/cesium/camera.js';
 import { annotationsFromParams, createView } from '../view/index.js';
 
 const EMBED_VIEW_MESSAGE = 'gev:view';
@@ -147,21 +148,19 @@ const delay = (ms, signal) =>
 function flyTo(viewer, camera) {
   announceNavigationAuthority('embed-view');
   return new Promise((resolve) => {
-    viewer.camera.flyTo({
-      destination: Cesium.Cartesian3.fromDegrees(
-        camera.lon,
-        camera.lat,
-        camera.altitude_m,
-      ),
-      orientation: {
-        heading: Cesium.Math.toRadians(camera.heading_deg),
-        pitch: Cesium.Math.toRadians(camera.pitch_deg),
-        roll: 0,
+    cameraOf(viewer).flyTo(
+      { lon: camera.lon, lat: camera.lat, height: camera.altitude_m },
+      {
+        orientation: {
+          heading: Cesium.Math.toRadians(camera.heading_deg),
+          pitch: Cesium.Math.toRadians(camera.pitch_deg),
+          roll: 0,
+        },
+        durationS: FLIGHT_SECONDS,
+        onComplete: () => resolve(true),
+        onCancel: () => resolve(false),
       },
-      duration: FLIGHT_SECONDS,
-      complete: () => resolve(true),
-      cancel: () => resolve(false),
-    });
+    );
   });
 }