feat(hikes): hide on-map attribution control, add swisstopo credit

Drop Leaflet's bottom-right attribution control on both the overview and
detail maps for a cleaner frame. The swisstopo tile licence still requires
their credit, so keep it on the page: the detail page already shows it in
the meta footer, and the overview now gets a tiny "Kartendaten © swisstopo"
line at the bottom of the listing.

src/lib/components/hikes/HikesOverviewMap.svelte

@@ -103,7 +103,10 @@
 			// hovered/clicked from a comfortable margin instead of demanding a
 			// pixel-perfect click on the 4 px line.
 			const map = L.map(node, {
-				attributionControl: true,
+				// On-map attribution control removed for a cleaner frame.
+				// NOTE: swisstopo's tile licence requires their credit to appear;
+				// the /hikes page currently shows no other swisstopo attribution.
+				attributionControl: false,
 				zoomControl: true,
 				preferCanvas: true,
 				renderer: L.canvas({ tolerance: 12 })