feat: add map center and zoom state management with URL synchronization

frontend/src/lib/components/FullMap.svelte

@@ -38,6 +38,7 @@
 	export let mapClass = 'w-full h-full';
 	export let standardControls = true;
 	export let zoom = 2;
+	export let center: [number, number] = [0, 0];
 	export let mapClickEnabled: boolean = true;
 
 	// Basemap
@@ -128,12 +129,25 @@
 		mapClick: { lngLat: { lng: number; lat: number } };
 		markerClick: { feature: unknown; markerProps: Record<string, unknown> | null };
 		clusterClick: LayerClickInfo;
+		mapMove: { center: { lng: number; lat: number }; zoom: number };
 	}>();
 
 	function handleMapClick(e: CustomEvent<{ lngLat: { lng: number; lat: number } }>) {
 		dispatch('mapClick', e.detail);
 	}
 
+	function handleMapMove() {
+		if (!map) return;
+		const mapCenter = map.getCenter();
+		const mapZoom = map.getZoom();
+		if (mapCenter && typeof mapZoom === 'number') {
+			dispatch('mapMove', {
+				center: { lng: mapCenter.lng, lat: mapCenter.lat },
+				zoom: mapZoom
+			});
+		}
+	}
+
 	function setBasemapType(next: string) {
 		basemapType = next;
 	}
@@ -261,7 +275,14 @@
 		{/if}
 	{/if}
 
-	<MapLibre bind:map style={getBasemapUrl(basemapType)} class={mapClass} {standardControls} {zoom}>
+	<MapLibre
+		bind:map
+		style={getBasemapUrl(basemapType)}
+		class={mapClass}
+		{standardControls}
+		{zoom}
+		{center}
+	>
 		{#key styleNonce}
 			{#if effectiveGeoJson && Array.isArray(effectiveGeoJson.features) && effectiveGeoJson.features.length > 0}
 				{#if clusterEnabled}
@@ -331,7 +352,9 @@
 		{/key}
 
 		{#if mapClickEnabled}
-			<MapEvents on:click={handleMapClick} />
+			<MapEvents on:click={handleMapClick} on:moveend={handleMapMove} />
+		{:else}
+			<MapEvents on:moveend={handleMapMove} />
 		{/if}
 		<slot name="overlays" {map} />
 	</MapLibre>

frontend/src/routes/map/+page.svelte

@@ -6,6 +6,7 @@
 	import type { ClusterOptions } from 'svelte-maplibre';
 	import { goto } from '$app/navigation';
 	import { getActivityColor } from '$lib';
+	import { page } from '$app/stores';
 
 	// Icons
 	import MapIcon from '~icons/mdi/map';
@@ -30,6 +31,11 @@
 
 	let basemapType: string = 'default';
 
+	// Map state from URL params
+	let mapZoom: number = 2;
+	let mapCenter: [number, number] = [0, 0];
+	let updateUrlTimeout: NodeJS.Timeout | null = null;
+
 	export let initialLatLng: { lat: number; lng: number } | null = null;
 
 	let visitedRegions: VisitedRegion[] = data.props.visitedRegions;
@@ -350,7 +356,40 @@
 		newMarker = null;
 	}
 
+	function updateUrlParams(lat: number, lng: number, zoom: number) {
+		if (updateUrlTimeout) clearTimeout(updateUrlTimeout);
+		updateUrlTimeout = setTimeout(() => {
+			const params = new URLSearchParams($page.url.searchParams);
+			params.set('lat', lat.toFixed(6));
+			params.set('lng', lng.toFixed(6));
+			params.set('zoom', zoom.toFixed(2));
+			goto(`?${params.toString()}`, { replaceState: true, noScroll: true, keepFocus: true });
+		}, 500);
+	}
+
+	function handleMapMove(e: CustomEvent<{ center: { lng: number; lat: number }; zoom: number }>) {
+		const { center, zoom } = e.detail;
+		updateUrlParams(center.lat, center.lng, zoom);
+	}
+
 	onMount(() => {
+		// Initialize from URL params
+		const params = $page.url.searchParams;
+		const lat = params.get('lat');
+		const lng = params.get('lng');
+		const zoom = params.get('zoom');
+
+		if (lat && lng && zoom) {
+			const parsedLat = parseFloat(lat);
+			const parsedLng = parseFloat(lng);
+			const parsedZoom = parseFloat(zoom);
+
+			if (Number.isFinite(parsedLat) && Number.isFinite(parsedLng) && Number.isFinite(parsedZoom)) {
+				mapCenter = [parsedLng, parsedLat];
+				mapZoom = parsedZoom;
+			}
+		}
+
 		if (typeof window === 'undefined' || typeof window.matchMedia !== 'function') return;
 		const mql = window.matchMedia('(hover: none), (pointer: coarse)');
 		const update = () => {
@@ -359,11 +398,17 @@
 		update();
 		if (typeof mql.addEventListener === 'function') {
 			mql.addEventListener('change', update);
-			return () => mql.removeEventListener('change', update);
+			return () => {
+				mql.removeEventListener('change', update);
+				if (updateUrlTimeout) clearTimeout(updateUrlTimeout);
+			};
 		}
 		// Safari < 14
 		(mql as any).addListener?.(update);
-		return () => (mql as any).removeListener?.(update);
+		return () => {
+			(mql as any).removeListener?.(update);
+			if (updateUrlTimeout) clearTimeout(updateUrlTimeout);
+		};
 	});
 
 	// FullMap handles cluster theme styling + cluster expansion on click.
@@ -465,7 +510,10 @@
 							{getMarkerProps}
 							mapClass="w-full h-full min-h-[70vh] rounded-lg"
 							standardControls
+							zoom={mapZoom}
+							center={mapCenter}
 							on:mapClick={addMarker}
+							on:mapMove={handleMapMove}
 						>
 							<svelte:fragment
 								slot="marker"