feat(hikes): route-builder, overview map + cards, SAC-coloured pipeline

Build pipeline (scripts/build-hikes.ts) parses per-hike GPX, encodes
images via sharp, reverse-geocodes the centroid against Swisstopo and
emits a typed manifest under src/lib/data/hikes.generated.ts (gitignored).
Track JSON + image binaries live outside /static; served in dev by a
small hike-images plugin in vite.config.ts, in prod by nginx (private/
images proxied through Node + X-Accel-Redirect for auth-gating).

/hikes overview: full-bleed Swisstopo hero map (HikesOverviewMap) sits
under the sticky nav, drawing one polyline per route coloured by SAC
tier (T1 yellow Wegweiser, T2/T3 white-red-white, T4-T6 white-blue-
white). Click navigates, hover thickens + tooltips. Layer toggle,
recenter, GPS controls mirror the detail map (minus images toggle).
Cards drop the trail SVG, gain a per-route icon + SAC marker
pictogram on the cover, altitude range, season label, and "Neu" badge
for recently-published hikes. Filter bar + totals strip recompute over
the currently-visible set.

/hikes/[slug]: hero map with elevation profile, photo strip with map
sync, scroll-position pin, GPX download, SAC marker stats + min/max
altitude + season.

Route-builder (/hikes/route-builder): client-side draft persisted to
localStorage, EXIF-driven image placement, snap-to-route via BRouter
(OSRM + linear fallback) and Swisstopo profile.json elevation
enrichment that handles degenerate same-coord segments via the height
endpoint.

Filter init switched from a script-time snapshot of data.hikes (which
sporadically returned a one-hike subset during dev hydration and
locked the page to that single hike) to a post-mount \$effect.

Content under src/content/hikes/ intentionally not included (WIP).

svelte.config.js

@@ -1,11 +1,19 @@
 import adapter from '@sveltejs/adapter-node';
 import { vitePreprocess } from '@sveltejs/vite-plugin-svelte';
+import { mdsvex } from 'mdsvex';
 
 /** @type {import('@sveltejs/kit').Config} */
 const config = {
-	// Consult https://kit.svelte.dev/docs/integrations#preprocessors
-	// for more information about preprocessors
-	preprocess: [vitePreprocess()],
+	extensions: ['.svelte', '.svx'],
+	preprocess: [
+		vitePreprocess(),
+		mdsvex({
+			extensions: ['.svx'],
+			layout: {
+				hike: 'src/lib/components/hikes/HikeMdxLayout.svelte'
+			}
+		})
+	],
 	kit: {
 		// adapter-auto only supports some environments, see https://kit.svelte.dev/docs/adapter-auto for a list.
 		// If your environment is not supported or you settled on a specific environment, switch out the adapter.