Fix: resolve data paths against app base for subdirectory deploys

The static app is served at /maps/ but the data manifest and graph/poi/layer
fetches used absolute /data/... paths, which resolved to the server root and
failed. Add src/lib/base.ts exporting upath() that prefixes a path with the
runtime-detected base (mirroring SvelteKit's 'base: new URL(".", location)'),
and apply it to the manifest, layer, graph and POI fetches. Works at both
root and any sub-path.

src/lib/base.ts

@@ -0,0 +1,27 @@
+// Base-path-aware data URL resolution for the Navigator static app.
+//
+// The app is built with the static adapter and deployed to a subdirectory
+// (e.g. /maps/). Its built index.html auto-detects the base from location
+// (base: new URL(".", location)), so all internal asset/data fetches must be
+// prefixed with that same base. Data manifest paths are stored as absolute
+// (/data/...) by the build scripts, so we resolve them against the running
+// location rather than the server root.
+//
+// E.g. served at https://site/maps/ -> base '/maps'; the manifest path
+// '/data/_index.json' becomes '/maps/data/_index.json'.
+
+export function appBase(): string {
+  if (typeof window === 'undefined') return '';
+  // Mirror the SvelteKit runtime detection: base = directory of the current
+  // page, with the trailing slash removed (so '/' -> '', '/maps/' -> '/maps').
+  const dir = new URL('.', window.location.href).pathname;
+  return dir.replace(/\/+$/, '');
+}
+
+// Resolve a path that may be absolute ('/data/x.json') relative to the app's
+// base. Leaves already-relative and non-leading-slash/dotted paths untouched.
+export function upath(p: string): string {
+  if (!p) return p;
+  if (p.startsWith('/')) return appBase() + p;
+  return p;
+}

src/lib/components/MapView.svelte

@@ -9,6 +9,7 @@
 	import { prefs } from '$lib/prefs';
 	import type { RouteGraph, AvoidRule, RouteResult } from '$lib/routing';
 	import { savedPoints, addSavedPoint, removeSavedPoint, exportSavedPoints, importSavedPoints, type SavedPoint } from '$lib/savedPoints';
+	import { upath } from '$lib/base';
 
 	type FeatureCollection = {
 		type: string;
@@ -184,7 +185,7 @@
 		if (!layer || !layer.graphPath || !layer.poiPath) { routeGraph = null; hasRouteGraph = false; return; }
 		routeLoading = true;
 		try {
-			const [g, p] = await Promise.all([fetch(layer.graphPath), fetch(layer.poiPath)]);
+			const [g, p] = await Promise.all([fetch(upath(layer.graphPath)), fetch(upath(layer.poiPath))]);
 			if (!g.ok) throw new Error(`graph HTTP ${g.status}`);
 			if (!p.ok) throw new Error(`poi HTTP ${p.status}`);
 			routeGraph = await g.json();
@@ -420,7 +421,7 @@
 		try {
 			for (const layer of layers) {
 				try {
-				const res = await fetch(layer.path);
+				const res = await fetch(upath(layer.path));
 				if (!res.ok) throw new Error(`fetch ${layer.path}: HTTP ${res.status}`);
 				const fc: FeatureCollection = await res.json();
 

src/routes/+page.svelte

@@ -1,6 +1,7 @@
 <script lang="ts">
 	import { onMount } from 'svelte';
 	import MapView, { type MapLayer } from '$lib/components/MapView.svelte';
+	import { upath } from '$lib/base';
 
 	type AreaManifest = MapLayer;
 
@@ -10,7 +11,7 @@
 
 	onMount(async () => {
 		try {
-			const res = await fetch('/data/_index.json');
+			const res = await fetch(upath('/data/_index.json'));
 			if (!res.ok) throw new Error(`manifest HTTP ${res.status}`);
 			areas = (await res.json()) as MapLayer[];
 		} catch (e) {