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/source-map/lib/url-browser.js

@@ -0,0 +1,21 @@
+/* -*- Mode: js; js-indent-level: 2; -*- */
+/*
+ * Copyright 2011 Mozilla Foundation and contributors
+ * Licensed under the New BSD license. See LICENSE or:
+ * http://opensource.org/licenses/BSD-3-Clause
+ */
+"use strict";
+
+/**
+ * Browser 'URL' implementations have been found to handle non-standard URL
+ * schemes poorly, and schemes like
+ *
+ *   webpack:///src/folder/file.js
+ *
+ * are very common in source maps. For the time being we use a JS
+ * implementation in these contexts instead. See
+ *
+ * * https://bugzilla.mozilla.org/show_bug.cgi?id=1374505
+ * * https://bugs.chromium.org/p/chromium/issues/detail?id=734880
+ */
+module.exports = require("whatwg-url").URL;