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/read-wasm-browser.js

@@ -0,0 +1,22 @@
+"use strict";
+
+let mappingsWasm = null;
+
+module.exports = function readWasm() {
+  if (typeof mappingsWasm === "string") {
+    return fetch(mappingsWasm)
+      .then(response => response.arrayBuffer());
+  }
+  if (mappingsWasm instanceof ArrayBuffer) {
+    return Promise.resolve(mappingsWasm);
+  }
+
+  throw new Error("You must provide the string URL or ArrayBuffer contents " +
+                  "of lib/mappings.wasm by calling " +
+                  "SourceMapConsumer.initialize({ 'lib/mappings.wasm': ... }) " +
+                  "before using SourceMapConsumer");
+};
+
+module.exports.initialize = input => {
+  mappingsWasm = input;
+};