feat(hikes): unify below-map view transition into one sliding panel

The detail-page enter/exit transition previously slid only the metric
tiles up from the bottom — the wrapper had no background, so its
snapshot was transparent and no containing panel moved. The photo strip
also animated separately, sliding in from the right.

Wrap everything below the hero map (stage nav, photo strip, metrics,
tags, elevation, scroll area, footer) in one `.below-map` element with
`view-transition-name: hike-below-map` and an opaque background, so the
whole sheet — background included — slides up on enter and down on exit
as a single panel. Drop the obsolete hike-strip right-slide rules and
keyframes; rename hike-below-strip → hike-below-map.

src/routes/hikes/[slug]/+page.svelte

@@ -415,21 +415,22 @@
 		</div>
 	</section>
 
+	<!-- Everything below the hero map — stage nav, photo strip, metrics,
+	     tags, elevation chart, scroll area, footer — is wrapped in one panel
+	     so view-transitions slide the whole block (with its own background)
+	     up from the bottom on enter and down on exit. The hero map morphs
+	     separately above this. -->
+	<div class="below-map" style="view-transition-name: hike-below-map">
 	{#if hasStages && stages}
 		<HikeStageNav {stages} />
 	{/if}
 
 	{#if track && track.length > 0 && visibleImagePoints.length > 0}
-		<section class="strip-area" style="view-transition-name: hike-strip">
+		<section class="strip-area">
 			<HikePhotoStrip images={visibleImagePoints} {track} {stages} />
 		</section>
 	{/if}
 
-	<!-- Everything below the photo strip is wrapped so view-transitions
-	     can slide the whole block (metrics, tags, elevation chart, scroll
-	     area, footer) up from the bottom on enter and down on exit. The
-	     hero map and strip animate separately above this. -->
-	<div class="below-strip" style="view-transition-name: hike-below-strip">
 	<section class="metrics" aria-label="Tourendaten">
 		{#if hike.icon}
 			<img class="route-icon" src={hike.icon} alt="" aria-hidden="true" />
@@ -985,6 +986,15 @@
 		opacity: 0.55;
 	}
 
+	/* The whole below-the-map block. The solid background makes its
+	   view-transition snapshot an opaque panel, so on enter/exit the entire
+	   sheet (background included) slides up/down from the bottom rather than
+	   just the metric tiles appearing to float. */
+	.below-map {
+		position: relative;
+		background: var(--color-bg-primary);
+	}
+
 	.strip-area {
 		padding-inline: 1rem;
 		margin-top: 0.5rem;