Add progressive web app companion for cross-platform access

Vite + TypeScript PWA that mirrors the Android app's core features:
- Pre-processed shelter data (build-time UTM33N→WGS84 conversion)
- Leaflet map with shelter markers, user location, and offline tiles
- Canvas compass arrow (ported from DirectionArrowView.kt)
- IndexedDB shelter cache with 7-day staleness check
- Service worker with CacheFirst tiles and precached app shell
- i18n for en, nb, nn (ported from Android strings.xml)
- iOS/Android compass handling with low-pass filter
- Respects user map interaction (no auto-snap on pan/zoom)
- Build revision cache-breaker for reliable SW updates

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pwa/node_modules/leaflet/src/geo/projection/Projection.SphericalMercator.js

@@ -0,0 +1,44 @@
+import {LatLng} from '../LatLng';
+import {Bounds} from '../../geometry/Bounds';
+import {Point} from '../../geometry/Point';
+
+/*
+ * @namespace Projection
+ * @projection L.Projection.SphericalMercator
+ *
+ * Spherical Mercator projection — the most common projection for online maps,
+ * used by almost all free and commercial tile providers. Assumes that Earth is
+ * a sphere. Used by the `EPSG:3857` CRS.
+ */
+
+var earthRadius = 6378137;
+
+export var SphericalMercator = {
+
+	R: earthRadius,
+	MAX_LATITUDE: 85.0511287798,
+
+	project: function (latlng) {
+		var d = Math.PI / 180,
+		    max = this.MAX_LATITUDE,
+		    lat = Math.max(Math.min(max, latlng.lat), -max),
+		    sin = Math.sin(lat * d);
+
+		return new Point(
+			this.R * latlng.lng * d,
+			this.R * Math.log((1 + sin) / (1 - sin)) / 2);
+	},
+
+	unproject: function (point) {
+		var d = 180 / Math.PI;
+
+		return new LatLng(
+			(2 * Math.atan(Math.exp(point.y / this.R)) - (Math.PI / 2)) * d,
+			point.x * d / this.R);
+	},
+
+	bounds: (function () {
+		var d = earthRadius * Math.PI;
+		return new Bounds([-d, -d], [d, d]);
+	})()
+};