feat(route-builder): show live elevation profile under the map

Render ElevationProfile below the route-builder map, fed by the routed segments (elevations fill in as the swisstopo enrichment resolves). Add a $effect in ElevationProfile so its dataset rebuilds when the track changes live during editing.

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "homepage",
-	"version": "1.88.0",
+	"version": "1.89.0",
 	"private": true,
 	"type": "module",
 	"scripts": {

src/lib/components/hikes/ElevationProfile.svelte

@@ -247,6 +247,26 @@
 		chart.update('none');
 	});
 
+	// Rebuild the dataset when the track data itself changes — e.g. the route
+	// builder edits the route live. On the static detail page `track` is stable
+	// after its one-time fetch, so this runs once (no-op) and never again.
+	$effect(() => {
+		const pts = track;
+		const ck = cumKm;
+		if (!chart) return;
+		chart.data.datasets[0].data = pts.map((p, i) => ({
+			x: ck[i],
+			y: typeof p[2] === 'number' ? p[2] : null
+		}));
+		const b = xBounds();
+		const xScale = chart.options.scales?.x;
+		if (xScale) {
+			xScale.min = b.min;
+			xScale.max = b.max;
+		}
+		chart.update('none');
+	});
+
 	// Mouse-leave on the canvas clears the shared hover state so the map marker
 	// disappears too.
 	function onCanvasMouseLeave() {

src/routes/hikes/route-builder/+page.svelte

@@ -6,7 +6,9 @@
 	import WaypointDetailPanel from '$lib/components/hikes/route-builder/WaypointDetailPanel.svelte';
 	import ImageDropzone from '$lib/components/hikes/route-builder/ImageDropzone.svelte';
 	import RouteStatsBar from '$lib/components/hikes/route-builder/RouteStatsBar.svelte';
+	import ElevationProfile from '$lib/components/hikes/ElevationProfile.svelte';
 	import { assembleTrackPoints, buildGpx, type GpxImageWaypoint, type GpxTrack } from '$lib/gpx';
+	import type { HikeTrackPoint } from '$types/hikes';
 	import {
 		builder,
 		focusWaypoint,
@@ -271,6 +273,11 @@
 	// chevrons follows the table's numbering.
 	const placedWaypoints = $derived(builder.waypoints.filter((w) => !w.unplaced));
 
+	// Flatten the routed segments ([lng, lat, ele?]) into one track for the
+	// elevation profile below the map. Elevations fill in once the Swisstopo
+	// enrichment resolves; until then those points read as gaps in the chart.
+	const elevationTrack = $derived(builder.routedSegments.flat() as HikeTrackPoint[]);
+
 	const focusedIdx = $derived.by(() => {
 		if (!mapView.focusId) return -1;
 		return placedWaypoints.findIndex((w) => w.id === mapView.focusId);
@@ -477,6 +484,12 @@
 		</div>
 	</div>
 
+	{#if elevationTrack.length > 1}
+		<section class="elevation-row" aria-label="Höhenprofil">
+			<ElevationProfile track={elevationTrack} />
+		</section>
+	{/if}
+
 	<WaypointTable
 		{pendingPlacementId}
 		onRequestPlacement={startPlacement}