feat(hikes): phone-sized static hero variant for ≤560 px viewports

The wide static hero picks its zoom for a desktop-sized container
(fitWidth 1920), so on phones the bbox lands too zoomed-in: most of
the route falls outside the visible 400 CSS px band.

Build now emits a second pose per hero — rendered with fitWidth 400 /
fitHeight 480 onto a 1200² canvas — so the auto-fit zoom matches what
Leaflet picks at the same container size. Per-hike hero gains four
variants total (theme × viewport); overview hero gains two.

The page picks which `<img>` to show via a `max-width: 560px` media
query (no JS needed for the swap), and `matchMedia` decides which
pose to hand to Leaflet's first `setView` so the static→live cross-
fade aligns regardless of viewport.

Drive-by: replace the long-stale `hike.heroMapUrl` reference in the
detail page's track-loading fallback with `hike.heroMapUrlLight`.

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "homepage",
-	"version": "1.73.0",
+	"version": "1.74.0",
 	"private": true,
 	"type": "module",
 	"scripts": {