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/side-channel/index.js

@@ -0,0 +1,43 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+var inspect = require('object-inspect');
+var getSideChannelList = require('side-channel-list');
+var getSideChannelMap = require('side-channel-map');
+var getSideChannelWeakMap = require('side-channel-weakmap');
+
+var makeChannel = getSideChannelWeakMap || getSideChannelMap || getSideChannelList;
+
+/** @type {import('.')} */
+module.exports = function getSideChannel() {
+	/** @typedef {ReturnType<typeof getSideChannel>} Channel */
+
+	/** @type {Channel | undefined} */ var $channelData;
+
+	/** @type {Channel} */
+	var channel = {
+		assert: function (key) {
+			if (!channel.has(key)) {
+				throw new $TypeError('Side channel does not contain ' + inspect(key));
+			}
+		},
+		'delete': function (key) {
+			return !!$channelData && $channelData['delete'](key);
+		},
+		get: function (key) {
+			return $channelData && $channelData.get(key);
+		},
+		has: function (key) {
+			return !!$channelData && $channelData.has(key);
+		},
+		set: function (key, value) {
+			if (!$channelData) {
+				$channelData = makeChannel();
+			}
+
+			$channelData.set(key, value);
+		}
+	};
+	// @ts-expect-error TODO: figure out why this is erroring
+	return channel;
+};