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/electron-to-chromium/index.js

@@ -0,0 +1,36 @@
+var versions = require('./versions');
+var fullVersions = require('./full-versions');
+var chromiumVersions = require('./chromium-versions');
+var fullChromiumVersions = require('./full-chromium-versions');
+
+var electronToChromium = function (query) {
+  var number = getQueryString(query);
+  return number.split('.').length > 2 ? fullVersions[number] : versions[number] || undefined;
+};
+
+var chromiumToElectron = function (query) {
+  var number = getQueryString(query);
+  return number.split('.').length > 2 ? fullChromiumVersions[number] : chromiumVersions[number] || undefined;
+};
+
+var electronToBrowserList = function (query) {
+  var number = getQueryString(query);
+  return versions[number] ? "Chrome >= " + versions[number] : undefined;
+};
+
+var getQueryString = function (query) {
+  var number = query;
+  if (query === 1) { number = "1.0" }
+  if (typeof query === 'number') { number += ''; }
+  return number;
+};
+
+module.exports = {
+  versions: versions,
+  fullVersions: fullVersions,
+  chromiumVersions: chromiumVersions,
+  fullChromiumVersions: fullChromiumVersions,
+  electronToChromium: electronToChromium,
+  electronToBrowserList: electronToBrowserList,
+  chromiumToElectron: chromiumToElectron
+};