feat(directions): keyless A→B directions with turn-by-turn steps and FLY (#564)

Supersedes #219 by @spcpza, ported onto the current component layout with fixes from review.

Verified before merge: format, package boundaries, unit suite, build, and the browser tracking suite; a browser harness for the change where one applies; adversarial review applied.

Co-authored-by: spcpza <[email protected]>

src/app/layers/directions.js

@@ -0,0 +1,12 @@
+import { createApplicationDirectionsLayer } from '../../data/directions.js';
+
+/**
+ * Construct one Directions layer using the application scene owners.
+ *
+ * It takes no data source: a route is fetched from `/api/route` when the
+ * operator places both endpoints, so there is nothing to supply up front.
+ * @returns {object} A fresh layer instance for this catalog.
+ */
+export function createApplicationDirections() {
+  return createApplicationDirectionsLayer();
+}